The appeal of Rock Paper Scissors Flour is exactly what it sounds like. Regular RPS produces a winner and a loser, but for casual play the consequence of losing is abstract. Flour makes it physical and immediate. The loser gets a face full of it. There's photographic evidence. Everyone in the vicinity has a reaction.
The game plays exactly like standard RPS. One round, or best-of-three if you want to build some tension first. The winner gets the flour. The loser gets the flour in the face — either thrown directly or applied via bowl. The bowl approach is cleaner and funnier and reduces the risk of someone inhaling a cloud.
Flour is the traditional choice because it's the easiest to photograph, dramatic in impact but genuinely harmless, and available in every kitchen. Face powder works if you want less cleanup or want to match the consequence to an indoor environment where white flour residue on the walls creates problems. The physics are different — powder disperses more widely, flour tends to land in a more concentrated impact — but the game is the same.
The only real disadvantage is cleanup. Flour is messy, and depending on where you play, the cleanup time will substantially exceed the game time. The solution is to play outside, play at someone else's house, or make the loser responsible for cleanup as part of the stakes. The last option adds an additional layer of consequence that keeps the game interesting across multiple rounds.
It's a party game that works because the stakes are tangible and the execution is fast. Pick the location carefully, choose the flour quantity in advance, and commit to the result when it lands.