Ninja Sword Share definition Flag Sneaking up on someone when they're sleeping and slapping or stabbing them with your erection. I'd tried to snowball him earlier on, so when I fell asleep ,he slapped me in the mug with his fucking ninja sword. Ninja Sword by TedZeppelin March 3, 2007 0 0 Get merch Get the Ninja Sword mug. Buy Now — $32.95 See more merch