Why do you say there is no score? You'd sum up how often you thought of the game. But most people don't do that (since that's excessive for what's mostly a joke, and it would incur more losses every time you saw wherever you were tracking the score), so it's mostly honour system.

You could play a casual game of basketball or mini golf or whatever without actually keeping score, but that doesn't mean there's no score and no mechanic for it.