There was an old professor who started every class with a vulgar joke. After one particularly nasty example, the women in the class decided to walk out the next time he started.

The professor got wind of this plot, so the next morning he walked in and said:

"Good morning, class. Did you hear the one about the shortage of whores in England?"

With that, all the women stood up and headed for the door.

"Wait, ladies," cried the professor. "The boat doesn't leave until tomorrow!"