When it comes to resolving disputes, Rock Paper Scissors is the universally accepted solution. Sure, there's always the binary outcome of flipping a coin or the all-inclusive practice of drawing straws, but what if you don't happen to have a coin or a bunch of straws on your person? Why, you revert to Rock Paper Scissors, of course.
Of course, another thing that RPS has going for it over the other two is that it's pretty good fun. Before pocket gaming came along, if you were stuck in a lift or stranded at a train station with a buddy you might revert to the classic three-gesture game of second guessing to pass the time. It was grim.