Why do people feel the need to call everyone a hipster?

I was watching some Animal Collective videos and all the comments were about hipsters and the band being hipsters and such. I don't get it. Why are they hipsters? Why are their fans hipsters? Why do people feel the need to call them that because they happen to prefer a different kind of music? Who died and made them God of whats good and bad music, whats art and not art? It's just so annoying. Some people just have to ruin everybody elses fun.