A blonde Texas city girl marries a Texas rancher.  One morning on his way out to check on the cows in the fields, the rancher says  to Amy: "The artificial insemination man is coming over to impregnate one of our cows today.  I drove a nail into the two-by-four just above the cow's stall in the barn.  You show him where the cow is when he gets here, okay?"  And the rancher left for the fields.

After a while, the artificial insemination man arrives and knocks on the front door.  Amy takes him down to the barn.  They walk along a long row of cows and when she sees the nail, she tells him:  "This  is the one, right here."

Terribly impressed by  what he seemed to think just might be another ditzy blonde, the man  asks, "Tell me little lady, how did you know this is the cow to be inseminated?"

"That's simple. By the nail over it's stall," Amy explains very confidently.

Then the man asks, "What's the nail for?"

She turns to walk away, and with complete confidence, says: "I guess it's to hang your pants on....."