"Tell Owen and Alex to start throwing that hay or I'll pinch their necks with my farm hands."
Farmer: "Great show!" "Thump thump thump"
Weakling: "Hey why are you clapping like that?"
Farmer: "It's the only way I can son, farm hands"
The phrase has its origins in the agricultural industry, where farmers would often slap their cows hard to get their attention. This gesture is an adaptation, its primary intentions being to rouse the attention of females, and to treat them as if they were cattle.
"Last night while I was hooking up with this girl, I have her a huge farm hand. She'll be marked for at least two weeks."