There's a guy hitchiking along the highway, when along comes an
   18-wheeler. It pulls up, and comes to a grinding halt. The hitcher
   runs to the truck, reaches up, opens the door and jumps in. Inside the
   truck is the driver, and beside him is his pet monkey.
   
   "Great lookin' monkey, mate" said the hitcher.
   
   "Yeah, he's great company, and he looks after you as well. Take a look
   at this."
   
   Without further ado, the truckie winds up, and punches the monkey in
   the guts with all his might. The monkey dutifully bends down, unzips
   the truckie's fly, goes down and gets to work on the truckie at a
   vigorous pace. Once the captain of the Kenworth has unloaded his cargo
   all over the cabin, the monkey wipes him off, zips up his master's fly
   and sits back down in his seat in the cabin.
   
   "That's GREAT!!!" says the by now quite interested hitchiker. "Can I
   have a go??"
   
   The truckie looks across and replies, "Yeah sure, why not?"
   
   "There's only one thing though" says the hitcher.
   
   "What?"
   
   "There's no need to smack me in the guts so hard."