면 죽다

do that and youre dead

Literally, cause and death: 난초는 물을 많이 주면 죽어. 일주일에 한 번이면 돼 'overwater orchids and they die.' It is also how rules in stories and games are stated — [누군가는 뒤를 돌아보면 죽는다] 'whoever looks back dies.' And it is a threat, usually a joking one between people who know each other: 너 못 맞히면 죽는다! 'get this wrong and you're dead', 내가 회장 딸이란 거 말하면 죽는다.

Register: the threat use is casual, often joking