Heard this from a D.J.:
A guy walks into a bar. He sees an attractive person of the opposite gender and walks up to her. He said, "Hey, can I buy you a drink?" The gal stands up walks to the middle of the room and shouts, "WHAT DO YOU THINK I AM, A PROSTITUTE?" She storms out of the bar, and the guy, face completely red, orders a beer and sat in a dark corner. A few minutes later, the girl returns and came up to the guy. She says, "I'm sorry about that. I'm psychology major and I was just testing to see your reaction to what I just said." Then the guy stands up and walks to the middle of the bar and shouts, "FIFTY DOLLARS?" :-)