Someone may have already written about these, but I don’t find them interesting enough to do real research on, as must have been true for early observers of rising intonation in declarative sentences. (As in, “So I went to the mall? And saw my best friend? And we had lunch?”)
The first is pronouncing the sound that begins “thin” as the sound that begins the word “then.” In jargon, the initial consonant was unvoiced, and now it is voiced. (Your voice box buzzes when you make the sound of “then” but not “thin”). It is only for one word, as far as I can tell: “thank” and its derivatives. A lot of people say “thanks” or “thank you” with the “then” sound. I may have even heard this pronunciation for “Thanksgiving,” but that’s a rare word, so my memory may be off. We’ll see if it spreads to “thin,” “thigh,” “thief,” etc.
The second is much more pervasive: devoicing a final “z” sound into an “s” sound. Devoicing a final consonant is common cross-linguistically (and again, “z” buzzes and “s” doesn’t). For example, pronouncing “please” to rhyme with “fleece.” As with rising intonation, it’s most frequent among insecure girls, the more effeminate homosexuals, and those who live on the West Coast.
It is especially noticeable when it’s used as a plural marker. By default, the plural in English has a “z” sound, and only goes to “s” when the preceding consonant is unvoiced, as in “cats.” But when someone says “dogs” with an “s” sound at the end, it’s affected, since “g” is voiced and there’s no reason to use an “s.” We’ll see if this affectation becomes regularized, the way Americans under age 40 or 45 pronounce “Milan” to rhyme with “anon” rather than “Japan.”
There, the pretense may have been “we’re trying to sound more authentic in the native language spoken in that city,” in the way that obnoxious tourists now strive to “live like a Parisian” by renting an apartment for a week and go about their daily routine, only in Paris – the way an authentic Parisian would, in contrast to what those loathsome fellow tourists are doing over at the Louvre. *
In the case of “dogs with an s,” the affectation appears to me to be a way of sounding more girly, hence its immediate adoption by flamers. On the other hand, there may be no rationale behind it at all, and it may simply be a fashion statement – “I pronounce words differently from you, and I’m cool,” which prompts the wannabes to shift in that direction too. And the gays may go along with it for the same reason they might copy female clothing trends like wide-legged vs. skinny jeans – they’re what’s “in” right now, period.
* It’s fine if that’s how you want to spend your vacation, but no one else cares.