"Smiths Trouble" joke

Mr. Smith goes to the doctor's office to collect his wife's test results.
The lab tech says to him, "I'm sorry, sir, but there has been a bit of a
mix-up and we have a problem. When we sent the samples from your wife to
the lab, the samples from another Mrs. Smith were sent as well, and we are
now uncertain which one is your wife's. Frankly, it is either bad or
terrible!"
"What do you mean?"
"Well, one Mrs. Smith has tested positive for Alzheimer's and the other for
AIDS. We can't tell which is your wife."
"That's terrible! Can we do the test over?"
"Normally, yes. But you have an HMO, and they won't pay for these expensive
tests more than once."
"Well, what am I supposed to do now?"
"The HMO recommends that you drop your wife off in the middle of town. If
she finds her way home, don't sleep with her."