A week later, the guy visits his doctor complaining of a large green lump on the end of his penis.

The doctor does a thorough exam, then pulls down a weighty medical book and flicks through it till he finds what he's looking for. He looks up and says, "I'm afraid this is serious. We'll have to operate!"

"Operate?", exclaims the fellow, "Why, Doc? What's the problem?"

"Well," explained the doctor, "you know how boxers can get a cauliflower ear? You've developed the same sort of thing. You've got a brothel sprout."