Penis Ninja is the Ninja of the peen and is sometimes used to insult someone but mostly used as a reference for an awesome event that has happened.

It is also used as a random ninja attack phrase when trying to scare someone or when trying to invoke the spirit of the Penis Ninja"

the art of remembering an arousing occurrence or some porn you watched while masturbating, often handy if you have no porn or your in the shower

An assassin who uses stealth and guile to assassinate a penis, often causing death to the owner of that penis. Scissors, knives, razors, and fire are typical weapons of a penis ninja. An historical example of a penis ninja would be the woman who killed Genghis Khan by slicing off his royal penis. Lorena Bobbitt is a more modern penis ninja of note, although her intended target managed to survive and was reunited with it's body.

A person sent in deliberately to have sex with someone's girlfriend with the intention of her significant other catching them in the act so he breaks up with her.