To fuck someone while listening to fast metal music. Usually, the partners will be fucking to the speed of the song, wildly and not stopping. The partners will move around from the woman being on top at one second to where she is on the bottom the next. Only the greatest sexual performers ever can master the art of Thrashfucking.
"Dude, did you hear about that new kid?"
"No, what about him?"
"He totally mastered thrashfucking!"