And it wasn't a class about B rated porn

Madonna showed up at a college film class unannounced.

The students at Hunter College in New York probably thought something was up when security guards were hanging around a film class Tuesday.

Then, Madonna showed up.

The pop star was their surprise guest professor after the class had seen an advance screening of her tour documentary, "I'm Going To Tell You A Secret."

Hey, those who can't do, teach.