尻をまくる

けつをまくる, しりをまくる, ケツをまくるketsuomakuru

expression · godan verb

1. to suddenly assume an antagonistic attitude
2. to suddenly become defiant
3. to turn aggressive (in one's manner)
4. to moon
5. to point one's naked buttocks at someone
6. to give someone the brown-eye

Study it in Yanamino