"Give it a rest" joke

A chap had a very painful elbow. He went to see his own
doctor, who told him to rest it: no treatment was required, it
was just tennis elbow.
Rather dissatisfied, he decided to go to a new computer-based
medical service that had just opened up. He went inside the
building and found the terminal, but there were no people in
sight. The instructions told him to slide his credit card
through the slot, and that $150 would be debited. When he had
done this, he was asked screen after screen of questions about
himself, until eventually a specimen bottle appeared. The
instructions on the screen said, "Produce urine specimen and
pour into slot on left," so he did. A few seconds later, the
screen read:
Diagnosis: Tennis elbow
Treatment: Rest
Well, he wasn't happy. $150 wasted just to be told the same
thing again. He thinks, "I'm going to confuse the hell out of
that smug machine." He went home, took a bottle and put a
scooped-up turd from his dog, some of his daughter's urine, some
crankcase oil from his car and
some of his own semen into the bottle and mixed it thoroughly.
Then he went back to the computer.
He waved his card through the slot, answered the questions
again and poured his mixture through the slot when asked.
There was a very long pause.
About half an hour later, the screen read:
Diagnosis:
1. Your dog has rabies
2. Your daughter is pregnant
3. Your car is going to throw a rod
4. If you don't stop wanking, your tennis elbow will never get better.