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1.
The act of solving any and all problems through the use of voilence and smoke bombs.
Stop crying, ninja up, and hit him or her in the neck with a throwing star."This sentence can be used for any situation."
by bmoten November 13, 2010
 
2.
(nin-juh up) verb. The act of tying a black t-shirt to ones face and doint subversive activities. Usually used when stealing cigarettes or blowing up peoples cars.
Johnny Twobags - Man, Ame has a pack of Newports, but shes asleep and I'd have to crawl over her.

Mr. Dopey - You'd better ninja up and do that shit

*Johnny Twobags ties his shirt up and backflips off the ceiling.
by Lonus the Terror March 11, 2007