Ninjackoff Share definition Flag Jacking off or masturbating in a ninja-like manner, often in public places like bathroom stalls or school buses. You can go in the bathroom there, but be sure to ninjackoff so you won't be noticed Ninjackoff by Timelinemc March 3, 2011 0 0 Get merch Get the Ninjackoff mug. Buy Now — $32.95 See more merch