I quite like the punchline but the part of the story relating to the actual subject title is a bit weak. Thoughts?

A popular theme tune sung at the top of our voices whenever our RE teacher turned away from us to write on the blackboard. Naturally, as soon as he turned around to confront us, we shut up. And so on.
He also used to show us "religious" films that he'd taped off the telly. We particularly loved the ads, and would sing along to any that had a jingle. "FADS, FADS F.A.D.S FADS!" was a particular favourite. If we talked during the film, he would punish us by threatening to fast-forward through the commercial breaks.