Probably my favourite joke I ever learned, believe it's from Super Dave (May he rest in peace)
A guy walks into a bar, and sees a monkey in a cage behind the bartender.
The guy asks the bartender: "What have you got the monkey in the back for?"
The bartender replies: "I'll show ya, but you have to wait until everybody else has left."
So, the hours go by, and slowly but surely, all the other guests leave the bar.
When the two of them are left, the bartender beckons the guy over, and they go in the back.
"This is what the monkey is for." The bartender says.
He lets the monkey out of the cage, whacks him with a broomstick over the head, and the monkey begins sucking his ween.
"Woah!" The guy exclaims.
"Yeah, pretty good, huh?" The bartender replies. "You wanna try?" He offers.
The guy says "Yeah, sure, but don't hit me too hard!"