The instinct of women to instantly drop whatever good time they may be having if one of their girlfriends is upset. Doesn't necessarily need to be at a prom, but good luck having a prom with out it, as they are training grounds for acts of promraderie in later life such as at weddings and any night at a bar involving 4 or more women.
Guy 1: Dude where'd your date go?
Guy 2: Her and 12 of her friends took off to the bathroom after one of them got a drink spilled on her.
Guy 1: That's some serious promraderie.