Bloke rings up his doctor, "Doc, I think my son's got the clap. Thing is, the only person he's ever shagged is our cleaning lady."

"Don't worry, old chap, just bring him in and we'll sort it..."

"Thing is, doc, I've been shagging her as well and now I've got symptoms too..."

"Don't worry, both come in and we'll sort you out..."

"But doc, I think my wife's also got it..."

"Oh shit!" sez the doc, "That means we've all got it!"