The ninja jack. The act of jacking off silently (quickly in most cases) and without those around you knowing that you had even done so.

Usually refers to jacking off while someone is talking on the phone (I.e. a girlfriend calls and you rub one out while she talks about something random).
Girl: "Hey, so anyways my day blah blah blah"
Guy: "yup, sounds good"
Guy::touching himself/finishes::
Girl: "So- what do you think?"
Guy: "Sounds like a plan. We meet at your parents house for dinner tomorrow night"

Ninja jack successful.

Girl: "What's wrong- you sound winded"

Almost.
by The Noob Tuber April 2, 2010
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a person (typically male) who is skilled in masturbating without being noticed by those around him. term coined from SRK
The jack ninja was so stealthy, he managed to get his business all over that girl's back without her noticing.
by cynik February 16, 2004
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way of grooming a dog or sexual position. Dog: fold ears over head so they touch and put a ninja mask on him.

Sex: jump from top of pancakes and land perpendicularly on top of sexual partner. Also wearing a ninja mask.
"Here at west minstah we see Spuds with the "Ninja Attack Flap Jack."

"Baby, finish me! Do the Ninja Attack Flap Jack!"
by bill from ultimate fakebook February 19, 2004
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