butt rock
n.— «Who’s worse Tesla or REO Speedwagon?…In retrospect, at what concert are you most ashamed of banging your head? I was never—as my sports writing colleagues refer to it—a “butt rock” fan.» —“I’m gonna keep on loving REO” by Peggy O’Neill Independent Record (Helena, Mont.) May 1, 2005. (source: Double-Tongued Dictionary)