Something like, the salesman needs a place to stay for the night and the farmer says, well OK you can stay in my daughter's room and she'll use the porch sofa, but let me tell you something, my daughter is crazy horny and I need you to stay the hell away from her no matter what she tries.
The salesman agrees to these terms, and he's getting ready to settle into bed. Later, the farmer decides to test the salesman's word and tiptoes quietly and carefully in the dark, and nestles himself into the bed.
The next morning, the farmer is waiting at the kitchen table with a scowl as the salesman approaches. "I told you not to do anything with my daughter you son of a bitch. I snuck into the bed, and then you thought you were fucking her, well that was me."
"Huh?" replied the salesman, "What are you talking about? I felt bad that your daughter had to sleep on the porch so I traded places with her."