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)
by Duo47 March 2, 2009
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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."

by anthony calloway February 17, 2008
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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.
by the ham wallets February 12, 2012
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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!
by ksarmyguy December 21, 2008
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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!
by Grantino October 30, 2007
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To sneak into the bathroom while someone is mid-shower, take a shit, and exit, leaving only the scent of shit wafting about the bathroom on the steamy air to announce the shitter's presence.
"God dammit! Brian ninja shit me again."
by faton4paws June 22, 2014
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When you wipe after you shit and the paper comes out clean... Like the shit was never there... mysterious and stealthy...
I love it when I take a ninja shit... I only have to wipe once!
by Jfranklin February 27, 2007
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