Expanding slightly to say, “…not a lawful defense to murder in the jurisdictions of which I am aware.” :)

Never accept an invitation to play chess in the Idaho section of Yellowstone.

I surmise also to exercise caution when considering en passant in some but not all american correctional facilities. And certainly don't pronounce it with a heavy french accent if you must, as it might arouse suspicion, even if your immediate opponent seems reasonable. If you do attempt this and violence seems imminent, try saying you were just kidding and gently restore the pieces to their original position.

Could it be possible to exploit differences in how death is defined? What if one were to stop the heart of the opponent, and then immediately resuscitate them?