We actually had to have a before-class assembly so the principal could reinforce the fact that there was to be no grinding or bumping at the school dance. It was hilarious, and ended in a teacher flash-mob of 'don't stop believing' , but that's another story.
Personally I think the 'no-hats' rule is a bit stupid, but all schools enforce it. I live in a small farming town, how many gangs can we even affiliate with?