A game played on school buses for generations.
If at any point during a ride on a school bus, you spot a person resting their hand on top of a seat back, you can immediately slap set hand as hard as humanly possible.
In the process, you must scream "BUS GAME!", preferably on contact.
Prime field position for this game is the back of the bus, inherently making it a "Cool People" game.
(slap) "BUS GAME!!!!!!"
"Oh it's on pal..."