The Ninja King is a chess move where your King takes every other piece on the board, moving crazy and ninja-like (you basically grab the king and knock every other piece over). It can only be used if either you are check-mated, or the King is your only piece on the board.
Note: This is not actually a real chess move.
"Oh man, I almost won that game, then Frank pulled a massive Ninja King on me. Did not see that coming."
Bob: "Check Mate!"
Frank: "Oh yeah? well how do you like my NINJA KING!"
*Grabs king and destroys every other piece*