Joke

A man walks into a bar and says, "Excuse me; I'd like a beer."
The bartender serves the drink and says, "That'll be four dollars."
The customer pulls out a $20 bill and hands it to the bartender.
"I'm afraid I can't take that, Sir," says the bartender.
The man pulls out a $10 bill, and the bartender rejects that also. "What's going on here?" the man asks.
Pointing to a neon sign, the bartender explains, "This is a singles bar."