when having anal sex with a girl. After pulling out of her, and with bits of poop (poo) on your dick, you then flick it over her face, leaving poop dots.
When one takes an accidental shit in their pants, and then blaming it on a fictional character, sometimes refered to as just "someone", or the "Poop Ninja"
Can be used as a verb, as well as a noun, sometimes even both.
Example 1: Someone took a shit in my pants, I don't know who, and I don't know why, but this is an issue that needs to be addressed immediately
Example 2:
Jimmy to Ricky: Dammit! Look out man, The Poop Ninja is on the loose. He got me.