The husband waits outside while the doctor is diagnosing the wife.
She is still in the examination room when the doctor comes out to speak with the man.
"Sir, I have some bad news. Your wife has either Alzheimer's or AIDS."
"You can't tell which one? What am I supposed to do?"
"There is one thing that you can do... drive her out to the middle of nowhere and leave her there - if she comes back, don't fuck her."