I'm introverted, but I've learned a lot about handling social situations since I work in retail. For me it has a lot to do with confidence--yes, I too was one of those "weird kids" who got picked on in school because I didn't conform to anyone's standards but my own. Fortunately now that I've been out of school and among a group of people who are much less judgmental than my peers ever were, I've managed to overcome a lot of that perceived shyness. I still have my guard up most of the time, though.
I find it's very situational for me. Generally, the weirder someone is, the more comfortable I am around them.
I was actually rather surprised recently when I found myself hanging out with one close friend and essentially a group of strangers (some of his friends, who were all cosplaying and more than one of them was drunk) and I actually wasn't nervous about the situation at all. Very unusual for me, but it actually felt pretty good. And also three days at a major convention with literally thousands of people everywhere--no problems. Normally I'd be fleeing in the other direction as fast as possible lol, but since it was a group of people I am comfortable with (gamers, since I am one myself), the crowd size didn't matter at all.
Sometimes even around family I find the need to retreat and recharge after an hour or two, but I guess that's more because I'm so different from most of them. Not a black sheep per se, just that I have so little in common with anyone outside my immediate family. Found it kind of funny that I was more comfortable around people dressed up as assassins, aliens and cactuars than I do around people I'm related to. So I guess I'm not as shy around people as I thought I was, it just has to be the right situation. Probably because "normal" people still judge me and I find "weird people" to be much more tolerant and, frankly, interesting in general.