also: けつマンコ
noun
Vulgar slang term for the anus. Strongly offensive; used in crude or insulting contexts.
See also: マンコ
あいつ、マジでケツマンコがゆるいんじゃね?
That guy's asshole is seriously loose, isn't it?
そんなこと言うとケツマンコに指突っ込むぞ。
Say that again and I'll stick a finger up your asshole.
Compound of ケツ (butt, vulgar) and マンコ (vulgar term for vagina). The exact origin is uncertain, but it is a crude slang coinage.