A girl goes into the doctor's office for a checkup. As she takes off her blouse,

 the doctor notices a red 'H' on her chest. "How did you get that mark on your chest?" asks the doctor. "Oh, my boyfriend went to Harvard and he's so proud of it he never takes off his Harvard sweatshirt, even when we make love," she replies.

A couple of days later, another girl comes in for a checkup. As she takes off her blouse, he notices a blue 'Y' on her chest. "How did you get that mark on your chest?" asks the doctor. "Oh, my boyfriend went to Yale and he's so proud of it that he never takes off his Yale sweatshirt, even when we make love," she replies.

A couple of days later, another girl comes in for a checkup. As she takes off her blouse, he notices a green 'M' on her chest. "Do you have a boyfriend at Michigan?" asks the doctor.

"No, but I have a girlfriend at Wisconsin, Why do you ask?"