Farmer's Wife...
One morning before the farmer goes out into the fields, he leaves his wife a message...'The artificial insemination man is coming over later to impregnate one of the cows. Please show him which one it is. I've put a nail in the panel over the stall.'
When the man arrives Nancy leads him to the barn and points him to the cow in the stall with the nail hammered into the panel.
'So what's the nail for?' the man asks curious.
'Well,' Nancy replies, 'I guess it's where you hang your pants on.'