First seen in Bungie's HumpdayChallenge DOA4 edition. Meaning to be owned, or in the case of a noob, pwned, severely. Most typically by a ninja, or in a stealthy fashion possibly by an assassination, Halostyle.
"Joe got Ninjowned." from Bungie's article on the DOA 4 Humpday Challenge.
See humpday, own, owned, pwn, pwned, ninja, halo, bungie, bungie