also: しりをまくる
expression, godan verb (-ru)
become suddenly defiant; turn aggressive; get belligerent
Describes a sudden shift to a hostile, confrontational attitude, often in an argument or negotiation. The image is of someone metaphorically rolling up their sleeves (or buttocks) to fight.
話し合いの途中で、彼は急にけつをまくって怒鳴り始めた。
In the middle of the discussion, he suddenly turned aggressive and started yelling.
That politician quickly becomes defiant when cornered.
expression, godan verb (-ru)
moon someone; expose one's buttocks; give the brown-eye
Literally pulling down one's pants to show the buttocks as an insult or prank. The expression plays on the literal meaning of けつ (butt) and まくる (to roll up).
酔っ払った勢いで、彼は窓からけつをまくった。
Drunk and carried away, he mooned out the window.
いたずらで友達にけつをまくるなんて、子供っぽい。
Mooning your friends as a prank is childish.