When a woman or man has an orifice pumped full of semen and then manages to stealthily roll out of bed without spilling a single drop of seed on either the bed or floor during the trip to the bathroom to deposit said semen in the toilet.
I banged her rotten then she ninja teacup rolled her ass to the bathroom without spilling a drop of my immaculate seed!
Ninja Cum (verb) is the wholesome act opon which a man sneaks behinde a unknowing victim (usually female) to simulate the characteristics of a ninja. Than proceeds to ejaculate over the unknowing victim,
then vanish to avoid atention of the victim to the next target.
Example
Guy1: "Dude, you should totally ninja cum that chick over there!"
Guy2: **Sneaks to unknowing victim then ejaculates all over her then get away without being noticed**
Her: "Like OMG WTF, Who just cummed all over meeee!"