assninja 

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

assninja by Fukaface! March 26, 2019

assninja 

Stealthy like a Ninja but Clumsy like an Ass

" I snuck up behind this dude while playing Halo and then like a total AssNinja, I got excited and threw a grenade and ended up killing myself instead" :(

assninja by King Spaz January 19, 2011

assninja 

One who runs away after licking ass.

"Your mom is such an assninja. She ran away before I could pay her for one of her award-winning rimjobs."

assninja by Faust December 25, 2003

ass ninja 

One who engages in anal sex so quickly and stealthily that the other person is unaware that it has occured.

Bobby was in and out in 9 seconds. He is a true ass ninja.

ass ninja by FAH Q 2 January 20, 2006

bird ass ninja

a sensitive asian guy, an asian guy who likes birds

Leon is a real bird ass ninja, he gets upset when he is not svelte.

Leon likes birds, so he must be a bird ass ninja.

bird ass ninja by DrJK December 21, 2010

ass ninja 

ninja's that spontaniously spawn from ones ass.

'Goddam, i had a bit of trouble with some ass ninja's this morning.'

ass ninja by Prycey September 9, 2003

ass ninja 

A mythical being who exists to give people wedgies. As with the Tooth Fairy, Santa Claus and the Easter Bunny, the Ass Ninja visits all the little boys and girls in order to bunch their underwear at the worst possible times.

"Dude I totally just got visited by the Ass Ninja! Cover me while I pick my underwear out of my butt."

ass ninja by Dark_Angel August 25, 2012