One myth from my student days.
A female student was taking part in a biology class. The students were to swab the insides of their mouths, then apply the swab to a microscope slide. Then, students would identify the cell types. The female student couldn't identify one cell and asked the lecturer to help.
He comes over, looks down the microscope and declares: "that is a sperm cell".
The older I get, the more convinced I am that this never happened.