Ninjat 

A Ninjat is a part feline, part human creature. The species resulted from the union of a ninja and a cat. Ninjats are famous for their lightning fast reflexes and their ability to shoot claws out of their fingers. They were created by the U.S. government during WWII in order to beat the Nazis.

Person #1: Hey, what are these weird scratch marks doing on my curtain?

(Ninjat jumps out)

Ninjat: DIE, infidel!!!!! meowy meow meow!

Ninjat by JT30 March 5, 2010

Ninja Pinch 

To steal something from somebody using stealth. Without anybody noticing the act...

I like that pen of John's. I'm totally going to (Ninja Pinch) it, when he puts it down.

Ninja Pinch by MbØt~Mk.II® March 13, 2015

Ninja Pooping

The art of layering the surface of toilet water with toilet paper to minimize the sound of splashing.

That's the last time I have Taco Bell for lunch at work. Now I'm going to have to do some ninja pooping.

Ninja Pooping by Extra Mayo January 27, 2013

Stage Ninja 

A wannabe roadie. Usually has the clothes and the tats but no real skill. Constantly boasts about where he has worked or how long he has been in 'the business'. Criticizes others openly but never offers an opinion of his own. Often carries a large quantity of useless keys to look important.

Get rid of these stage ninjas and get me some stage carps who know their stuff

Stage Ninja by dingoetmybaby November 5, 2019

Ninja Nude 

The act of fully undressing and taking a nude in a classroom, meeting, lecture or other busy event. Almost impossible to accomplish without getting caught.

James tried to take a Ninja Nude during the lecture for his girl and got his stupid ass caught!

Ninja Nude by UrbanDict is life July 13, 2016

pirate-ninja

a kilowatt-hour per martian day

Mark Watney created the pirate-ninja as a standard unit

pirate-ninja by knafb;lkfbvaklfndbknlF;LKNVDLB July 3, 2015

The Law of Inverse Ninja Strength 

When confronted by ninja(s), the individual ninja will be far more powerful than a group of ninjas. To see the effectiveness of a group of ninjas simply use the equation power= 1/n, where n is the number of ninjas

Don't worry about the group of 1,000 ninjas, worry about the single guy, according to The Law of Inverse Ninja Strength

The Law of Inverse Ninja Strength by jamundertoast December 17, 2010