There are just some subjects which naturally possess bawdy comedic value. For instance, students taking “repro” classes–where labs involve heading out to the farm, getting the animals excited, and collecting ejaculate.
One student had told her professor about a conversation she had with her straight-laced mother who had expressed some horror about the labs. In response, the young woman had replied, “Well, that wasn’t the first time I’ve had semen on me.”
D’oh! That’s just not something your mother wants to hear.