Halloween

Keying cars is a rather more vicious act, using a key to scratch the paint of on a car.  Not a practice that I often associate with normal Halloween pranks, but obviously Principal Snyder has a low opinion of Buffy.

Bobbing for apples on the other hand, is often associated with Halloween but is not a prank.  Rather, it's a game where the contestants attempt to bite an apple that is floating in a tub of water, without using their hands.  The practice is certainly innocent fun when compared to the rest.  Perhaps Principal Snyder is showing just how out of touch he is.