We give nicknames to very few things around us, only those that are close enough to sustain and enrich our lives that we feel the need to individuate them from all the other clutter in our lives. Our pets are the most obvious example. Naming newborn or unborn children is common, but not everywhere. In some places where infant mortality is high, mothers don't even name their children until they reach a certain age. Not naming them right after birth (or even before) is a way to keep from growing too attached to them and then feeling demoralized should the child die within the first couple years of life. This makes it easier for the mother to move on with things and start again.
Back when young people had a life, guys used to name their cars in the same way that they used to christen ships or give names to their horses. It was a vehicle for physical freedom, and as a token of gratitude you gave it a name to pick it out against all those other cars that weren't so special. Since the early 1990s the percent of 17 year-olds who have a driver's license has been plummeting, and within the last few years it finally slipped below 50% -- today the typical 17 year-old does not have a license. Let alone have access to a car, especially one that is only theirs.
The LA Times ran a feature story on this major shift in the early 2000s, and my own experience talking to Millennial guys matches that -- namely, they view cars mostly as a burden and a hassle. Driving a car is no longer the holy grail for the freedom-seeking American teenage guy, which makes sense since, not having a life, they don't really have anywhere to go or anything to do in the back seat like guys used to. I haven't seen any survey data on this, but obviously the percent of teenage guys who give a name to a car has fallen sharply; the only question is by how much.
After some googling, I found that plenty of guys today name their Xbox video game console, their iPod, iPhone, Mac laptop, etc. I'm not talking about cases where the technology allows you to register a name for it, like how you can have your computer referred to as "Darwin" instead of "My Computer." I mean where they christen the thing and refer to it that way in their own natural speech. Again there was no survey data that I could find, so how common this is I don't know. But I do know that no one nicknamed their phone when I was a teenager, or their computer, or their video game system.
This shows the larger shift that young people have undergone: they used to value the greater physical freedom that a car could deliver, while now they value the greater informational or virtual freedom that comes from farting around on the internet via your iPhone or playing Halo (both alone or online). They then give names to the vehicles that take them to the places they value most.
Not that I talk to Millennial guys an awful lot, but I'd wager dollars to donuts that almost none of them have given a proper name to their cock. Before, it wasn't as though everyone did that, but it was common enough to hold a place in the folklore and folkpractices of young guys. Millennial guys are so afraid of expressing their libido, though, and are generally grossed out by the physical nature of sex -- "Ewwww, she's got pubic hair! Mommy, tell her mommy to make her shave it off!" And statistics on sexual behavior show that they're far less wild than young guys used to be (the decline starts in the early 1990s, as with wild behavior in general). Put all of those pieces together, and I can't see that the old practice of naming it has survived.
For the same reasons, I doubt guys who have a girlfriend give names to her anatomy either. Obviously even in wild times this was less common than naming your own, since every guy had his own junk but not all had a girlfriend, and it's a bit of a risky move to give her parts their own names, since girls aren't as salacious as guys. * Still, today this folkpractice of young people must be entirely dead.
This decline in wildness is what's behind the observations about the lack of emotional depth that young people have in relationships today, like girls who are busy texting furiously even when they're grinding some guy on the dance floor. After all, it takes quite a close emotional bond for a girlfriend and boyfriend to share a pet name for her pussy. A subset of this phenomenon is all the worrying about the "hook-up culture," which is actually a sign of Puritanical rather than Dionysian sex lives. Among young people, there's less sex, it happens later, and with less of a sense of magic pervading it.
* To show that happened at all, I wanted to refer to a popular movie where this happens, but I can't remember the name or the overall plot. The scene shows a woman listening to an answering machine message, where an ex-boyfriend or ex-husband is trying to win her back by reminiscing about their fun times together. (Or perhaps he's there in the room with her?) He reminds her of how they named both her left and right tit, as well as her pussy, supplying the names for all (which I forget). She has a somewhat embarrassed, somewhat amused look on her face, like Sigourney Weaver does when Bill Murray charms her over in front of Lincoln Center in Ghostbusters. I tried finding this movie through google, but you can guess what sort of results I got instead. Anyone know which one I'm talking about? Seems like it was from the '80s through the mid-'90s.