The worst kind of metal fan? Hmmm I'd have to say the old schoolers who don't or won't listen to anything new. It's seems like they stopped in 1995.
Alot of the metal "fans" my age(mid 30's) are guilty of this. I wouldn't even call them metal fans personally. Stop living in the past. There's so much more out there than "Crazy Train", "Run to the Hills" and "Master of Puppets". I love the classics but I'm always out looking for new music.
On the flipside it has to be those dopes who dress like robbers in the pits. lol I wanna smash them in the face lol. Or those idiots at Children of Bodom shows who play the air keyboard lol