Guy with a sore elbow goes to the Doc and says, "Doc, I've got this sort right elbow, I think it's because..."
"STOP", said the Doc, "I don't want you trying to diagnose your own problems, otherwise you wouldn't be here, if you knew what the cause was. I've just bought this super-duper diagnostic computer that requires you to give me a urine sample - but it has to be the first p!ss of the day, so take this sterile bottle home, and bring it back to me tomorrow."
"But I think it's only because I..."
"STOP! You are NOT a Doctor - just take the bottle and come back tomorrow.
Being a bit p!ssed off at having to come back again, the patient decides he'll teach the Doctor a lesson.
He takes the bottle home and gets his daughter to squirt a sample into it, then his wife, the family dog, and finally he ejaculates into it for good measure.
The next morning he returns to the Doctor with his "sample".
"Here you are Doc - what's your diagnosis?"
The Doctor takes the bottle over to the new super-duper diagnostic device, and tips it in.
Very quickly, a sheet of paper is churned out.
The Doctor reads through it and then looks at his patient.
"Yes Doctor?", asks the smirking man, "What is the result?", almost unable to contain himself from bursting into laughter, thinking about the contents of the bottle.
"Well sir, your daughter's pregnant, the wife is having an affair with the milkman, your dog has gout, and if YOU don't stop w@nking you'll never get rid of that sore elbow!"