A professor told dirty jokes in class and the women wanted to protest it. So they decided that in the next time that the professor will start with these kind of jokes they all will leave the class as a protest.

Somehow the professor heard about the plan.

In the next lecture, in the beginning of the lecture he said: "In Sweden a prostitute makes $2000 per night."

All the women stood up and started to leave the class. So he shouted after them: "Where are you going? The plane to Sweden doesn't take off until the day after tomorrow."