look up any word, like fleek:
 
1.
To penetrate another person without that person having knowledge or noticing.
Person 1: Whoa what was that?
Person 2: You just got ninja fucked!
by mario420 September 06, 2006
 
2.
To have sex in a quick and intense manner.
"I could tell by the look on her face that she got ninja-fucked last night."
by Jordy-Time February 16, 2006
 
3.
To have sex in a bunk bed without your bunkmate noticing.
Dude, I ninjafucked this girl last night. My roomie had no idea. I guess he likes being rocked to sleep.
by mizzou22 November 20, 2008
 
4.
If I heard this right, it refers to the action of being sexed half-willing, whether out of obligation or whatever motivation (this isn't referring to rape, mind you). It comes from a movie called Dog Park, and I'd like to see the term used more.
"How'd it go last night? Well, she ninjafucked me."
by geoffy mcgee August 05, 2004
 
5.
When you ( a male) is having sex with two other people ( male or female) and you fuck them in the butts back to back. Hence, you see an ASS, you see an ASS, and you went IN, or assassin ( which is a word used to describe a ninja).
Joe Schmoe: Hey bro, I just had a consecutive buttsex with these two smoking hot chicks last night
Douchebag Dan: Duuuuuude! You just had a Ninja Fuck!!!
Joe: Totally gnarly dude!!
by Jdawg96 December 17, 2013
 
6.
wearing a black-body suit with only your dick n balls hanging out in a very dark room, drunk ho walks in u tap that shit with your baby dick, and peace out with her having no idea...ninjafucked.
God damn im so fucked up in ninjafucked.
by DirtyLightaOriginator June 11, 2010