A man walked up to a farmer's house, and knocked on the door.
When the farmer's wife opened the door, the man asked if she knew
how to have sex.  Not amused, she slammed the door. Again, the
man knocked, and again, he asked the same question. Again, she
slammed the door and screamed, "Get the hell away!"
Later, she told her husband of the incident. He said he would
stay home the following day just in case. Sure enough, the next
day the same man returned.
The husband hid with his gun while his wife answered the door.
When she was asked again if she knew how to have sex she said,
"Yes!"
The man replied, "Great! Give some to your husband the next time
you see him, and tell him to keep the hell away from my wife!