Make a donkey laugh. (Slightly NSFW)

There was a bar that was famous for giving out cash prizes if people could complete a challenge that the bar tender made up. One day, tired of losing wads of money, the bartender decided he needs an impossible challenge. He acquires a donkey and tells the whole town that there's a $1,000 in it for the man who can make his donkey laugh. This challenge is attempted by all in town, and then those from neighboring towns, but none could make the donkey laugh.

Then one day a stranger comes to town. He walks into the bar and asks if the challenge still stood. The bartender, smug from going undefeated, laughs and says, "Yeah. The donkey is out back. Good luck." The man goes out back and shortly afterward the bar is filled with this awful noise. The patrons all rush outside and the bartender follows. There they find the donkey rolling around on the ground and making a sound that is unmistakably laughter. The bartender hands the stranger his money in stunned silence.

The bartender, having a donkey and needing a new challenge, decides that this time the challenge will be to make his donkey cry. Again, none of the locals could succeed in making the donkey cry. But then the stranger returns and asks the bartender if the donkey is still out back. The bartender nods, and the man goes out back. Shortly thereafter the bar is again filled with a terrible noise. Everyone rushes out back to find the stranger standing next to a donkey that has dropped to its knees and even has tear falling from its face.

The bartender is about to hand the stranger his money. "But first," he says, "you must tell us how you did it." The man replies, "Well, when you wanted me to make the donkey laugh, I told him my dick was bigger than his. And when you wanted me to make him cry... I showed him."