A guy is in jail for a year, so to pass the time he catches a fly and teaches it to do tricks. He has it lay on it's back, jump into a matchbox, walk a little thread set up as a tightrope. He spends the whole year teaching the thing tricks.

Upon his release he goes into a bar and sits down. He opens the matchbox and lets the fly out. As the fly patiently sits there, he sets up the little tightrope and everything else.

He calls the bartender over and says, "Hey bartender, see this?"

The bartender goes, "Oh, sorry, dude." and squishes the fly with a flyswatter.