Someone who wears acid-washed or razor shredded jeans, sometimes sports a mullet, other times sports greasy ass hair. You will find them flashing devil horn signs while listening to Nelson ("(Can't Live Without Your) Love and Affection").
"Dude, you're dating a total butt rocker!
"Dude, what's a butt rocker? Is that someone that takes it from the back?" says the east coast chick.