A bloke in a bar downs a couple of beers, and the blond bartender informs him he owes $4. "But I paid, don't you remember?" says the customer. "Okay," says the bartender, "If you said you paid, you did." The man then goes outside and tells the first person he sees that the bartender can't keep track of whether his customers have paid.
The second man then ruses in, orders a beer and later pulls the same stunt. The barkeep replies, "If you say you paid, I'll take your word for it."
Soon the customer goes into the street, sees an old friend, and tells him how to get free drinks. The man hurries into the bar and begins to drink high-balls when, suddenly, the bartender leans over sand says, "You know, a funny thing happened in here tonight. Two men were drinking beer, neither paid and both claimed that they did. The next guy who tries that is going to get punched right in the nose."
"Don't bother me with your troubles," the final patron responds. "Just give me my change and I'll be on my way."