One Saturday evening a man walked into a bar and said, "Excuse me, I would like a pint of beer." The bartender served the man his drink and said, "That will be four dollars." The customer pulled out a twenty-dollar bill and handed it to the bartender.
"Sorry, sir," the bartender said, "but I can't accept that."
So the man pulls out a ten-dollar bill, and the bartender rejects his money again. "What's going on here?" the puzzled man asked the barkeep.
Pointing to a neon sign behind the bar, the bartender explained, "This is a Singles Bar."