A man walks up to a bartender and tells him “I bet you $5,000 I can pee into a cup all the way across your bar.”

The bartender, knowing this is impossible, agrees. They set it up and the man starts peeing all over the place, missing the cup completely. The bartender gets begins to cheer because he know he just won $5,000.
The man walks over to his friends and comes back to the bartender. He pays the bartender his money with a grin on his face. The bartender asks him “Why are you so happy? You just lost $5,000.”

The man replies “I know, but I bet my friends $10,000 dollars that you would cheer while I pee all over the bar.”