rhetorical question. “turn up” is the act of getting drunk and high and being reckless so “turn down” would mean sobering up. turn down for what is really saying i am fucked up and will continue to be all night no matter what. the only appropriate answer to this question would be “nothing”
Johnny: turn down for what ?!
Ben: The cops and my dad.
Johnny: You’re a pussy! TURN DOWN FOR NOTHING