There is silence, and then one guys gets up and leaves. Later on he re-appears, and asks the Yank if the bet is still on.
"It sure is" booms the Yank.
So 30 pints of Guinness are set up, and the Irishman downs the lot with 20 seconds to spare.
"Wow", yells the Yank, and hands him his $5000, before enquiring, "Why did you go out when I made the offer ?"
"Well", says the Irishman,
Spoiler:

