Post 1444 from the More Jokes Thread, posted by Lancia, who is a schoolteacher: It seems to be relevant here.
I just told this joke to my students because, hey, its a nice clean joke that’s totally appropriate for the classroom and everyone is still talking about the Super Bowl and football in general so why not. Little did I know they’d be able to one-up me (or you, as it so happens). As soon I tell the punchline a voice in the back row shouts out:
"Hey Lancia, what did Cinderella do when she got to the ball?
Me: Um… … hmm… …?
Student: She gagged.
Much laughter from the room, the boys making disgusting simian sounds and congratulating each other on their wicked sense of humor while I get to spend 2 or 3 minutes trying to get everyone back on track. That’ll teach me to tell an innocent joke in class.