A woman goes to her doctor and says, "I'm getting this rash all over my chest..."
The doctor says, "Ok, let's have a look..."
She removes her top and he can see the skin is red and a bit bumpy.
Stepping back, he notices the rash is perfectly in the shape of a large letter "M".
"Does your boyfriend go to Michigan?"
"Yes, he does...how did you know?"
"Well, does he wear his college sweater when you two are being intimate?"
She blushes a little and says, "Yes, usually...but how..."
"Look. The rash is in the shape of a letter 'M'. You must be allergic to the material the letter is made out of in the sweater."
He prescribes her some topical ointment and advises her to have him not wear that sweater when they're in close contact and she goes on her way.
---two weeks later---
A different woman comes in and complains of a rash on her chest.
"This sounds familiar" thinks the doctor. "Let's have a look."
She removes her top and, once again, he sees the perfectly shaped letter "M" in the rash.
The doctor immediately says, "Let me guess....boyfriend goes to Michigan..."
"No, my girlfriend goes to Wisconsin...why?"