I recall an IDPA stage from a few years back where you sat at a poker table, surrounded by targets with card suits (hearts, diamonds, spades, clubs) stamped on them. At the buzzer you drew a random card from the top of a deck conveniently placed on the table - the corresponding suit became 'no-shoot' targets, and everything else deemed hostile.
We still rib a friend who drew a card and then promptly shot the nearest target bearing the matching suit (and thus a friendly) with an outstanding controlled pair to the head, followed a split second later with an exclamation of "Kitten" once his brain caught up. Fun times.