뇌절 /noe-jeol/
Beating a dead horse / Overdoing a joke
Repeating a joke or bit way past the point where it's funny — literally 'brain fold.' Used when someone can't let a gag die.
Examples
그 드립 뇌절이야, 이제 그만해
That joke has gone way too far, stop beating the dead horse
뇌절 그만ㅋㅋ 이미 안 웃김
Stop overdoing it lol, it stopped being funny a while ago