But, no, I didn't make it up, it's a term [some] people use:
From Urban Dictionary:
1. BUTT ROCK
Butt rock is the any Heavy Metal music from the eighties that is so horrible that it is both hysterical and hella rad at the same time. These bands usually have amazingly ugly members who wear exceedinly tight pants big hair and make up. One good way to tell if a band is "Butt Rock" is if during their music video, the drummer blows a kiss to the screen while drumming
Quiet Riot and Twiztid Sister are the best examples of butt rock. If you really want to know about the radness of butt rock download the song "Cum on feel the noise!" by Quiet Riot
by rad kid Dec 11, 2003
My favorite butt-rock band, Guns 'n' Roses: