Rock-paper-scissors can only be improved when you can drop in a pair of extra, dorktacular options and hash it out with rock-paper-scissors-lizard-Spock.
Look, any fool can settle an unresolvable dispute with the invocation of rock-paper-scissors, but where is the nuance or subtlety in that? Don't settle for a mere three-point decision matrix — which means that in any two-player showdown, you always have a 66% chance of at least a draw — when you can drop in a pair of extra, dorktacular options and hash it out with rock-paper-scissors-lizard-Spock.
The rules are simple, as this Big Bang Theory video explains, but when in doubt, just refer to the handy t-shirt diagram, which explains that rock crushes lizard, scissors decapitate lizard, lizard eats paper, lizard poisons Spock, paper disproves Spock, Spock vaporizes rock, Spock bends scissors, and (as always) rock breaks scissors, scissors cut paper, and paper covers rock. Simple, right?
Just buy the shirt.