A guy was looking for a place to sit in a crowded university library.
He asked a girl: "Do you mind if I sit beside you?"
The girl replied in a loud voice: "NO! I DON'T WANT TO SPEND THE NIGHT WITH YOU!"
All the students in the library started staring at the guy; he was truly embarrassed and moved to another table.
After a couple of minutes, the girl walked quietly over to the guy's table and said with a laugh:
"I study psychology, and I know what a man is thinking. I guess you felt embarrassed, right?"
The guy then responded in a loud voice: "$500 FOR ONE NIGHT? ... THAT'S TOO MUCH!"
All the people in the library looked at the girl in shock.
The guy whispered in her ear: "I study law, and I know how to screw people".
(with thanks to Cathal Cavanagh.)