A professor told dirty jokes in class and the women wanted to protest¹ it. So they decided² 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."