Yeah, this is so common (most of all among hipsters) that it must just be an effect of human nature. I remember how amusing it was when Nirvana unexpectedly hit the bigtime and all the indie types who had been raving about them as gods suddenly were forced into "Nirvana sucks, they sold out" mode. Cognitive dissonance in action!

If other people steal the emblems of my identity (by liking the same band I like, or going to the same conference I do), it's as if they're stealing my soul. Worst case scenario, I might have to admit that I'm not that different from the average guy. That's a bitter pill for a lot of us, especially those who were raised with or otherwise acquired the idea that we're exceptional or superior.

An interesting irony about this is that the ego dynamic underlying it all is so primitive and so identical.