Both forms involve a mapping from inner feelings to outward expressions that is disingenuous. With transparent irony, an observer can still work their way back from expression to feeling, whereas opaque irony leaves the observer puzzled and confused about what feeling they should infer from a given expression.
Beginning in the early-to-mid '90s, ironic behavior primarily took the form of layering a veneer of distaste, ridicule, etc., over top of a feeling of enjoyment or approval. If you liked the guitar solo from "Sweet Child O' Mine," you had to re-enact it with the most caricatured air guitar solo of all time -- every time it played. Otherwise you were just plain old enjoying it, and that was suspicious -- you don't want the Expression Police to knock on the door, do you? Then do the ridiculous air guitar thing, and it'll provide a fig leaf of plausible deniability if they show up on your front porch. "Nah man, I was just like, *making fun of* those cheesy '80s guitar solos. You don't think I'd actually dig something so ridiculous... so uh, am I cleared to go back inside now?"
That was also the time when we started to cultivate an anti-style, wearing things that were so far from our inner, core identity that it was like going out in blackface. Rebellious teenagers wearing musty-looking cardigans -- wacky! But, not confusing, no more so than a well-heeled white performing in blackface during the Jazz Age. I had an anti-authoritarian streak in high school, so the first election season that I could vote, 1998, I found some old Nixon/Agnew pins to wear on my field jacket.
So, we made fun of the stuff we liked, and appeared to endorse things we wanted nothing to do with. Once you knew that shift in mindset, though, you could then figure out how we felt from what we expressed -- just infer the opposite of what you normally would. Why did we make observers go through this mental rotation task every time they wanted to figure out what we really meant? Again, it provided plausible deniability when the Expression Police came to our door.
In times when normal behavior becomes criminalized, and warped behavior elevated, being a normal rebellious young person was suddenly like being a dissident in an authoritarian state. Plaster the outside of your business with posters in support of the stodgy old leader, and put up dissident posters inside -- that have been suitably yet not blasphemously defaced. That was a fine line to walk back then -- how to poke enough fun in order to evade detection as a true supporter, while not going so far as to defile or disrespect your idols.
I associate this transparent irony with Family Guy and the early Simpsons on TV, and grunge and alternative music, both how they sounded on the radio / album, and how their videos looked on MTV. Family Guy and bands like Weezer show how this form might lead toward the sentimental -- when you have an official cover of not liking something, you might give yourself free rein to (inwardly) indulge in it way more than if you were just being sincere.
Irony-squared, or opaque irony, is a different beast altogether. Any given expression of enjoyment is as likely to have come from a positive as a negative feeling. And any expression of ridicule could just as well come from truly enjoying it as it could from truly hating it.
Does that selfie of you with a kabuki "angry" expression mean you're truly angry or just goofing around? Who can tell -- you make that face equally often in angering and in uplifting circumstances. Expressions are indiscriminate. Ditto for the kabuki "elated surprise" face -- you make that when you just found out you got a pay raise, as well as when you're at your own mother's funeral.
I picked up the same vibe from Millennials who got into the whole '80s revival in the mid-to-late 2000s. Were they wearing those clothes from American Apparel because they really liked the style, or was it another case of blackface ("check it out, cheesy '80s fashion")? It was as likely to be one as the other.
Emotional expression in indie music is indiscriminately neutral and "bleh," and it is indiscriminately angsty in emo. Most singer-songwriter stuff takes the form of indiscriminate attention-seeking through constant signals of needing to be rescued -- the musical equivalent of "the boy who cried wolf."
This impossible-to-pin-down character is not just a switcharoo to fool the authorities. In the '90s, we were all in on the joke -- whether we thought the put-on was subversively cool or just plain annoying, we could still decode the underlying feeling from the expression. Young people these days can't figure out how the hell anybody else is feeling, what they actually like, what they truly despise, and what they really mean. Plausible deniability is no longer a smoke-screen for when the Expression Police roll up, but a pervasive fog that atomizes the entirety of the younger generation (and anybody attempting to interact with them).
You see this especially clearly in their awkward "social" lives. They prefer gathering together in a hive, like a computer cluster at the campus library, or any of the other public spaces that have been converted to that purpose, like coffee shops. They'll make glance at / make eye contact with people they're interested in, but will then look randomly around the room too -- as though to suggest that nothing in particular steered their eyes to the person they made eye contact with. Then they stay hunkered down over their glowing screens, whether there's someone there they're interested in or not. It's indiscriminate looking-around or indiscriminate shutting-the-blinds.
Same thing on Facebook and texting, where they prefer even more to "interact." Does some boy like some girl? Well, maybe Boy will work up the courage to leave an interested yet non-committal comment on Girl's wall (or whatever that retarded thing is called now). But wait, will Girl interpret that as an honest signal of Boy's interest? Uh... uh... shit, I know, let's leave a cover-your-ass comment, too, just in case. "....hashtag unintentionally awkward Facebook comments." Great! Now she'll never know how I really feel about her! Dodged a bullet there...
And it's not just pussified boys who act that way. If random Millennial boys came up to talk to a Millennial girl at Starbucks, she'd get creeped out. Whether they were subtle or obvious wouldn't matter, and would only determine how quickly she'd scurry away. If they went on Facebook / texted her, openly telling her how they felt about her, she'd get creeped out if it were "attracted," and outraged if it were "concerned and critical." Better just shut up about how you really feel, no matter what that may be.
The inscrutable nature of Millennial signal-sending leads to profound confusion not only of what others feel, but about one's own worthiness. If you can't tell where your peers truly rank you for attractiveness, trustworthiness, fun-loving-ness, etc., then what are you to do? You can try to make up the answer yourself -- "obviously I'm in the top 1%, just like everybody else" -- but your brain isn't that stupid. It knows that the answers must come from peers, not family or ego, in order to not be biased, and particularly from a wide range of peers, rather than only those who have a motive to kiss your butt, or only those who want to tear you down.
With no signals coming in that can be at least somewhat pinned down, the data are simply not entered at all. It's as though all the surveys about you came back filled entirely with "Chose Not To Answer." This is worse than having a wide margin-of-error -- that at least provides an estimate in the center somewhere. This is like all blank answers, or maybe "illegible" answers is more apt.
This is at the root of all sorts of dysmorphias among young people today. Not just body dysmorphia from not knowing how attractive your peers find you. Any quality of yours is subject to self-doubt and unending anxiety about what all those missing answers would have contained if people would just say what they honestly felt.
Kids these days are hesitant to approach and reluctant to respond, and it's a positive feedback loop. As the signal-sender, they give indiscriminate signals, which tells the other side not to get involved with them -- no point if you can't tell what they mean. Then, even if someone else gave them a clear signal for a change, as the signal-receiver they wouldn't know how to respond. With greater experience, you develop a knack for how to respond in situation A, B, C, and so on. And you judge how appropriate your response was by how the other party responded in turn. But since you've never gotten feedback on your feedback, you don't know how to react even when the situation is clearly A. So you just pick a response at random -- another indiscriminate choice, when you have no clue what to do.
That clumsiness frustrates the other side -- "I open up for once, and this is what happens. I'm such an idiot for bothering in the first place. Guard up forever." Interpersonal awkwardness will never go away so long as the drive toward opaque irony remains in place.
Millennials do occasionally get together as friends or boyfriend-girlfriend. But none of the "courtship" can refer to feelings. It's all about how "we would make sense together." (Feel the passion sizzling off of the page.) It's just a fact that your qualities and my qualities would produce a mutually beneficial arrangement. I think some of them are hoping that after the initial agreement has been made, they can shed the contractual / for-hire way of interacting with each other and talking about their relationship. But once you've chosen that mindset, it's hard to choose another. Cognitive dissonance, fear of the unfamiliar, general awkwardness, etc.
So they stay in relationships as long as they agree to renew their contract, or as long as they can convince one another that they still "make sense" as a couple. They do lapse into the occasional expression of genuine affection, and given how rare it is, they'll likely remember that for the rest of the relationship. On the whole, though, the contractual frame of mind makes for a spirit-crushing atmosphere, and they are easily estranged from each other.
It should be clear that I trace both forms of irony back to the cocooning trend of the past 20 or so years, and that openness and sincerity came back starting in the late '50s or so and peaked in the '80s. What about before then? I pick up the same vibes from the mid-century as from today. The hipsters today are incredibly marginal figures, and an observer from 60 years in the future might have trouble tracking them down. But everybody knows about the Beatniks from the mid-century. Was their malaise just a put-on (transparent), or were they indiscriminately disaffected (opaque)? Beats me, seems like both, though.
And then there was all that cracking wise -- was the wise-cracking a put-on, or did they crack wise no matter whether they enjoyed or loathed what they were commenting on? Was the wise-cracking dame truly interested in you, or was she as likely to crack wise if she hated your guts too? Ditto all the wise-cracking from the fellas. In that environment, better to just not show much feeling at all, and hunker down in your own little world (The Man in the Gray Flannel Suit, The Feminine Mystique). Mid-century Americans have an inscrutable quality, where they're either indiscriminately chipper (campy ads where the whole family is wearing a big gay smile), or indiscriminately morose (the Existentialist, Hopper, Age of Anxiety, Beatnik crowd).
Inequality and competitiveness were falling and near a low-point, so at least they didn't make status contests out of ironic displays like we do. Or at least not to the same extent -- they still had all those layers upon layers of wise-cracking between men and women in both film noir and in screwball comedies, to see who would gain the upper hand. Just give it a rest already, you buncha fast-talkin' broads...
* * *
I considered including a helpful mathematical analogy in the main post, then I figured it wouldn't be that helpful to most people -- would drive them away. If that's you, you can split now.
For those who remember functions from algebra class, we can think of sincerity, irony, and irony-squared as three simple types of functions that map feeling (on the x axis) into expression (on the y).
Sincerity is something like f(x) = x, an increasing function through the origin. The only important thing is that positive feelings lead to positive expressions, negative feelings to negative expressions. It passes both the horizontal and vertical "line tests," so it is invertible -- from a given expression, you can tell what feeling produced it.
Transparent irony is like f(x) = -x, a decreasing function through the origin, and orthogonal to the sincerity function. We can rotate the axes 90 degrees and obtain the sincerity function, and then we're back to the first case. It's as though people rotated the axes, then applied the sincerity function. OK, we'll just rotate the axes back, and then invert the sincerity function.
So we can still recover the feeling that produced a given expression. It just requires an extra step that makes it annoying for most people to bother with, especially strangers who don't really care much about how we really feel. The orthogonality of these first two functions gives the second one a shock value, but one that wears off quickly as we learn to apply a simple axis rotation first.
Opaque irony is like f(x) = x^2 (or -x^2), and f(x) = |x| (or -|x|), concave up (or down) with a minimum (or maximum) on the y axis, and symmetric about it. This passes the vertical line test -- every feeling leads to a certain expression. But it fails the horizontal line test, and so is not a one-to-one correspondence that would let us invert it. For any expression, there are two possible feelings that could have produced it -- and they're opposite in sign and equal in magnitude.
Axis rotation is no help this time: rotating 90 degrees would yield something that wasn't even a function, a relation that took a given feeling and was equally likely to express it in a positive as a negative way. We are stuck with expressions only, uncertain whether a positive or a negative feeling produced them.
This isn't just a nerdy exercise, an analogy for its own sake. I think each of these formal properties of the model reflects something real about how the mind works. Like doing mental rotation of the axes when transforming the transparent irony function into the more familiar sincerity one. That rotation would also swap which one was feeling and which one was expression -- part of that whole post-modernist playing around with / questioning of / inversion of the surface and substance that was a big thing at the time, at least among those who were also pushing the (transparent) irony thing at the same time.