Top Definition
Undeniably one of the sneakiest and scariest ASSassins of the world. Known for being able to PENETRATE the most secure facilities in the world with incredible ease with the sole intention of raping man ass. Butt ninjas have super human abilities allowing them to walk through walls, turn invisible, cling to ceilings, and run faster than light... translation: they will have sex with your butt no matter what.
Bro-1: "I was too afraid to shower at the empty gym last night. I kept thinking I saw a butt ninja out of the corner of my eye."
Bro-2: "That's a lie, a butt ninja would've never gotten spotted by a douche like you. Probably just a normal rapist."
by pokstad January 25, 2008

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A karate butt humper
"woah! i just got raped by a fucking sneaky butt ninja! i hate my life!"
by poopOnsatan April 26, 2003

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Asian buttpirates
AGH! The buttninja are attacking! COVER YOUR ASS!
by Brian Blake December 10, 2003

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one who is a sneaky a-hole & hard to spot before it's too late, yet considerably annoying on every level that no one wants to be around...usually due to them just being an idiot & not being able to help their own stupidity..
"That guy who showed up at the last minute to go out with the rest of us is such a buttninja!...we HAVE to ditch him!!
by NomadJr November 04, 2010

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An incredibly pungent fart that occurs without warning.
I was in the middle kissing her when this BUTT NINJA comes out of nowhere and kills the mood! I was so embarrassed.
by MR.ZERO July 24, 2011

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The Urban Dictionary T-Shirt

Soft and offensive. Just like you.

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The Urban Dictionary T-Shirt

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The state of a ninja where you rape people's butts
"dude my butt just got raped..."
"By who?"
"I have no clue"
"Maybe it was a butt ninja"
by theylimek May 11, 2010

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The Urban Dictionary T-Shirt

Soft and offensive. Just like you.

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The Urban Dictionary T-Shirt

Smooth, soft, slim fit American Apparel shirt. Custom printed. 100% fine jersey cotton, except for heather grey (90% cotton).

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