He says he'll give $100 to anyone who can drink 10 pints of Guinness in a row.
No one takes up the offer, but one bloke in the back, quietly gets up and leaves.
A while later, a guy taps the American on the back and asks, "Hey mate, is that deal about drinking 10 pints of Guinness for $100 still on?"
The American looks at the Irishman and says, "Yeah, it still is. By the way, aren't you the guy who left the pub when I first told about the deal?"
The Irishman, looked shamefully down and said, "Aye mate, that was me."
"Well, where did ya go?" The American asked.
"I went to the pub next door and ordered 10 pints of Guinness and them all in a row!"