I was once at a very indie film festival which had some very indie bands playing before the films started, and the hot-pink-haired lead singer of one of the bands had a Hannah Montana shirt. To this crowd, that sent an unmistakable message: "Ha ha, why am I wearing this shirt, clearly I'm one of you because there's no way I could be serious about liking Hannah Montana."

On the other hand, it would signal coolness or at least normalcy to certain parts of the "conventional culture" (specifically, young teenage girls who actually do like HM, and older people who think that's a normal sort of thing for them young folks to like, and who don't distinguish much between wildly different subgroups of young folks).

That's the general formula, though usually for it to work specifically as SirBacon described, the relevant subset of "conventional culture" needs to be larger. But when it's not — if you're going around in your Hannah Montana shirt and there are a lot of people who neither take it as non-ironically positive nor are aware of the intended irony, and consequently look down on you — it still works, though in a different way: you get to gain even more status among your indie/hipster friends when you tell them about that stupid mainstream chump who didn't get the joke. (However, getting that kind of response might also feel good for reasons unrelated to status — comparable, perhaps, to internet trolls who relish the angry/disgusted/eye-rolling responses they get from people taking them seriously, even if they are completely solitary and anonymous, leaving them no chance of being lauded by other trolls for their success.)

Why Can't Anyone Tell I'm Wearing This Business Suit Ironically?

Hipsters

http://www.nytimes.com/2010/02/19/opinion/19brooks.html

Link is to David Brooks, an elite columnist for an elite paper, chiding "elites". He gets paid for this stuff, and is presumably read in earnest by millions of Americans.