A woman goes to the doctor complaining of bad knee pains. After the diagnostic tests showed nothing, the doctor questions her, "There must be something you're doing that you haven't told me. Can you think of anything that might be doing this to your knees?"
"Well," she said a little sheepishly, "my husband and I have sex doggy-style on the floor every night."
"That's got to be it," said the doctor. "There are plenty of other positions and ways to have sex, you know."
"Not if I'm going to watch TV, there ain't," she replied.