noun
Colloquial term for the anus; can be used in casual or vulgar contexts.
あいつ、転んで尻穴を強く打ったらしい。
He fell and apparently hit his anus hard.
noun
Derogatory term for a contemptible person; strong vulgar insult.
あのケツメド野郎、また嘘つきやがった。
That asshole lied again.
Compound of 尻 (けつ, 'buttocks') and 穴 (めど, variant of あな, 'hole'). The reading めど is an older or dialectal form of あな.