The irony is that most of them are really concerned about what other people think of themselves. One person, upon me telling them a joke that they found to be in bad taste, proclaimed it to be unoriginal, that they'd heard it before, and thusly not funny. No, you haven't heard it before. The real issue was that they found it unfunny and rather than rely on their opinion, they offset it to something more easily defendable - that they'd heard it before. But also, because you're the center of the universe, anything you deem unfunny must irrevocably be unfunny.
Some of them, I think, develop this as a defense mechanism. You're afraid that what you are isn't good enough, so you retreat into a place in your head where you are all that is. If you are all that is important, you can deal with your constant perceived failings. And what results is someone who truly believes they are the only cool kids around. You end up with the person that defends everything like it is a personal attack and usually from the standpoint that they are correct no matter what. But at the same time, anyone with any insight knows that this person is constantly looking in the mirror for their own imperfections.
I think too many people see the world in a self-centric perspective. It is easy to believe that everything revolves around you when you're standing still. Too many people don't step outside of their own perceptions and belief strata to realize what other people realize, find funny, think, etc. The world is bigger than you and your preferences.
And I don't think the internet is helping this in the least. People are both marginalized by their myspace profiles and at the same time, uplifted into perceived stereotypes by them. To quote almighty Chuck, I am more than my friends list, music preference, and marital status. But I'm not sure if other people know that they are. I've met someone who was interesting and intelligent and had great conversation skills that stopped talking to me cold turkey because I had the gall to laugh at her endless sub-genre categorization of music. I'm sorry that I thought Post-Rock had vocals because Sigur Ros is considered to be post-rock and they sing. Oh my god, get over yourself. I later came to believe that her knowledge of the insane x-core heraldry of music was probably her only way to be better than everyone else and thus, very important to her pysche.
I think that if you convince yourself that you're cool, not only will you believe it but, eventually, you'll start treating everyone else as less-than. And I think the more you become self-centered, the more you are defined by the increasingly small outward descriptors of your preferences. If you're reading this and you fear it might be about you, read about existentialism and gain some fucking perspective. This post is already too long and yet, I don't think I've hit on exactly what I set out to say. Oh well, maybe more later. I'll work on something positive for the next one, I think