That's once!
 

A newlywed country farmer was driving his horse and buggy back from the wedding and the horse stopped suddenly. The farmer climbed out of his buggy and gave the horse a stern look and said "That's once" climbed back into his buggy and snapped the reins and the horse started trotting again.

However after a few more miles, the horse stopped again. The farmer climbed out of his buggy and approached the horse and said "That's twice" climbed back into his buggy and snapped the reins and the horse started trotting again.

After a few more miles the horse stopped another time but this time the farmer grabbed his shotgun and put the horse down. And the wife started freaking out and yelling at him "Are you stupid?!? We are in the middle of nowhere, miles from our home and you shot the horse! Now what?!?"

Farmer just gives a stern look at his wife and says, "That's once!"

I grew up with that joke! :D