One who is stealthy like a ninja, jumping from one ass to another (usually raping them, usually a gay ninja too).
They could be a figurative assninja, or a real gay ass ninja!
The
latter would dress up as a ninja, with
stars and
everything, and perform ass sex with kunais, advanced forms of taijutsu, ninjutsu and genjutsu.
They are to be feared when they possess a sharingan!
John walked oppenlegged, ass bleeding out of his bedroom this
morning. He had a swarm of assninja's on his back all
night, and won't be able to sit for a month now!
Yeah, one of the rapists was Gay-Sensei