I had to explain to a male coworker, one who is married and has a kid, that women don't have prostates, therefore we won't cover a Prostate Specific Antigen test for a woman. Trying to be as delicate as possible, I had to explain that the prostate is part of the equipment that makes a male a male. Feeling increasingly desperate because he was still clueless, I said "It's just like a guy won't have a cervix."
When he asked me what a cervix was, I told him to ask his wife. My manager overheard my side of the conversation with her jaw open because she couldn't believe I had to explain the difference between boy bits and girl bits to a guy around my age (36ish).
I misread that as, "women don't have potatoes"
A friend of mine was in her first year of med school. The topic of the tutorial happened to be human puberty or something similar, and the tutor was kind of rushing through the obvious stuff that everyone knows to get to the more important details that they would need to know as doctors. But then one guy raised his hand and interrupted...
"Hang on, did you say that during menstruation, blood comes out constantly? For days?"
"Yes, that's pretty much the biggest symptom of menstruation. Anyway-"
"No, no, I mean, constantly
? Come on!"
"What do you mean? Of course it's constant; they can't just turn it off and on for convenience anymore than you can turn your heart off when you feel like it!"
The guy's jaw hit the ground. Apparently he thought it was just bloody urine. He had no idea that it occurred outside bathroom visits. I don't know if he finished med school. I've heard worse misconceptions, but not from med students.