You know how kids will draw out battlefields, and then sorta play out the scene by having everything shoot at everything else? My kid was doing a version of that, and I suggested adding dice into the mix. The result was a hilarious improv rpg.
I played "Pomo, the Monster from Asteroid Tomato Area." I'm not too sure what the rules were. There were lots of dice pools and jets of acid and it all ended in a TPK.