One who can masturbate/masturbates everywhere they have gone/are without fear of being caught, with any object, without being seen, heard, or others having suspicion of the action of masturbation, any where, any time, and any place.
Student #1: Hey man, I whacked off in biology today.
Student #2: HOLY HELL! Did you get caught?
Student #1: Hell no I didn't, I am a freaking Masturbation Ninja.
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Guy #1: I jizzed all over my friends moms bra last night while he was in the same room.
Guy #2: What!? He didn't see you?
Guy #1: Shit no, he was sleeping.
Guy #2: Good thing you're a Masturbation Ninja.
Guy #1: Damn right.
by gregmastersensai November 19, 2009
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A ceramic fragment, usually from a broken spark plug, used to break car windows for petty thievery.
The ninja rock popped the cork on the brand new 540i, and we grabbed an ID and a checkbook.
by JP July 27, 2004
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A ninja-turd occurs when your feces has the rare but precise trajectory to exit your anus and travel directly into the toilet pipe so that when the defecator turns to examine his/her excrement it remains hidden as if it was never there...(like a ninja)
Defecator: Wow I just pooped, let me see what I did.
(Stands to turn and look)
Where did it go? I know I pooped, but its just not here...ahhhh damn you ninja-turd!
by KingDestiny GS '11 November 20, 2008
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One who can have sex with a herpies infected person several times and still come out clean.
I'm a Ninja I'm a Herpes Ninja!
Man I got away with sleeping with that cuz I'm a Herpes Ninja.
I can sleep with her cuz I'm a Herpes Ninja.
by omega123180 February 26, 2010
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When someone is about to perform oral services to a male, the male tucks his penis between his legs when the performer isnt paying attention. When the performer's face is close enough to the penis the male opens his legs, resulting in a surprise attack to the performer's face.
Johnny did the "hidden ninja" on Hailey, and she broke up with him.
by Sergiee Bear October 18, 2007
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Someone who practices parkour or freeruning.
Dude didja see that freakin urban ninja do a backflip offa that building!?
by m dog dd March 25, 2006
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1. noun - cockblocking maneuver involving the unauthorized entry of an unclothed male into a room occupied by two or more people currently hooking up or having intercourse. the 'ninja' employs dramatic body action (e.g. jumping into a room with wide open arms) and a verbal cue (e.g. "naked ninja!")

Additional Notes: It could in theory be done by a female but such action might be desirable.

2. verb - the act of being a naked ninja
Step 1. Remove all clothing

Step 2. Find a bedroom where two people are hooking up or having intercourse

Step 3. Subtly determine if the door is unlocked, if it is unlocked go to step 4, if not, go to step 3a.

Step 3a. Unlock the door by any means necessary while preserving the element of surprise

Step 4. Throw the door wide open

Step 5. Leap into the room with a signature body gesture and scream "naked ninja" ensuring that your genitals are in plain view.

Step 6. Run like Hell
by Strider Hiryu March 29, 2006
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