Because I feel that I have to spend most of my time defending the genre. With all the morons I deal with on a daily basis, the scene-fucks who think they're metalheads, and the pseudo-metalheads and whatnot. I keep having to correct people for calling a certain band metal because I want some people to actually have an idea of what it is. They think that anything heavy is metal.
So yeah. I tend to be a dickhead when I explain things. Like when one kid found out I was a metalhead, he asked me, "do you like wecamewithbrokenteeth?" I said "Hahahahah. No! That", in which he asked why. So then I said "because they're a shitty scene band".
He seemed to have meant well, but at least he knows (or probably got the idea) that they're not metal.