He who shits in close proximity to others without being noticed.
Guy 1: Who in the hell shit on my shoe?
Guy 2: Looks like we have a Shit Ninja on our hands!
Someone who sits in a public toilet taking a shit as silently as possible, not moving around or making any noise, with the intent of catching someone doing something embarrassing thinking they are not there.
It is usually a good idea to duck down and check for shit ninjas before you do something that would otherwise be considered embarrassing.
Joe: *walks into bathroom, thinking nobody is in there*
Joe: FUCK, that slutty little bitch was SO motherfucking hot! But too bad she's only twelve years old! *slams wall with fist*
*sound of rustling toilet paper*
Joe thinks: (Oh god, it's a shit ninja)
Mike: *walks into bathroom, thinking nobody is in there*
Mike: I gotta take a massive fucking dump! *FAAAAAART*
*sound of someone shifting around on a toilet seat cover*
Mike thinks: (fuck, not another shit ninja)
The evil bandits that shit in one's mouth over the course of a night, leading to the not-so-fresh feeling we all know as morning breath. The ninjas camp out longer after one participates in a night of drinking or other elicit activity.
Man, the shit ninjas really got me last night.
The art of taking a shit or farting without your boyfriend, husband or roomates knowing you did so. Only females can be shit ninjas
"Dude my wife is a shit ninja, we've been married 2 years and to my knowlege she hasnt shit once."
what douchebag video game nerds call you when they cant think of anything else to say.
video game nerd: why did you trip me down the stairs jackass?
me: fight me?
video game nerd: you know what! YOUR A SHIT NINJA!