The music board on 4chan. Most of the music discussed on /mu/ is avant garde-experimental-noise-indie bullshit that nobody's heard about. /mu/ users (often called /mu/tants) will flame anybody who likes anything else. Although there is a modest community of metalheads on /mu/ they are generally disliked by the obscure taste flaunting majority that inhabits the board. Basically, it is a big contest to see who listens to the most obscure bands. The less people have heard of the music you listen to, the better.
I went to /mu/ the other day. Never before have I seen so many pretentious tight-wads in a single board.