In high school one of my friends, who was super preppy, always wore khakis. Let’s call him James.
One day in class another friend, Vince, saw James’ khaki-ed butt sticking out while he was bending over someone’s desk talking to them.
Vince does a huge wind up and spanks him so hard on the butt that he immediately jumps up. The problem is that the person was not James, but our teacher. Everyone is mortified, especially Vince, and the teacher’s face goes bright red. The teacher just says “Vince! Save that for AFTER class” with a big grin on his face.
Everyone just busts out laughing, except for Vince, of course.