When you disappear behind a thick puff of smoke. Works better with a hookah; inhale the smoke and then slowly breathe out. Make sure to be standing near a place where you would hide yourself.
Ambrose - Okay guys, check it out! (creates a huge smokescreen and disappears behind the curtain)
Buds - WTF? This dude must be a fucking ninja!
by Ambrose Zeppo December 04, 2009
incredible game in which players bow toward one another to start the game and then each player makes one move at a time, in a clock wise manner. the object of the game is to hit the opponent(s) hand. the last person standing is declared the ULTIMATE ninjaaaaaaaa...
these games lead to awkward positions by all players, most of the time very homosexual.

often a lunch time pass time for jasons, manuels, sebastians, and franciscos.
Person 1: dude, what do you want to do?

Person 2: lets play Ninja!

Person 1: hell yeah!
by the_ninjirate November 14, 2009
To do something slyly or discreetly; to act in a secret manner.
Dood 1: "Dood, did you see Bob jack that old lady's purse?"
Dood 2: "Yeah, dood, Bob is sooo ninja."

"Dude. Next time, try to be ninja when you steal a cookie from the cookie jar. Jeez.."
by MJ is cool. August 07, 2009
A term used to describe dominating an opponent by sly or sneaky means of assault. Usually used to describe killing someone from behind before they realise what is occurring. Popularized by competitive gaming culture, in particular Halo 3.
"The guy thought he could kill me, but I hid around the corner and ninja'd him."
by Correct Spelling July 05, 2009
vb. To steal something out a window or whilst spinning.

Not to be confused with plain theft, to ninja something you must take it and throw it out a window or jump out the window with it, OR you must spin past it and pick it up mid-spin so as to make the action invisible to the human eye.
He totally ninja'd that chair out the back window.
by death on yee. February 28, 2009
In a forum, one who posts while another is still typing his post, making the latter's post seem repetitive or confusing.
dang it! bob ninja'd me and made me look like a total idiot that repeats everything he says!

dang, there are so many ninjas here that the whole thread makes no sense!
by tylertheoutcastzombie May 13, 2008
a rhyming derivative of Ginger... ie a Redheaded person.
"watch out here comes a Ginger Ninja" or "Nobody likes Ninjas"
by zkpilot March 09, 2008

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