A guy was celebrating his birthday. He and his wife weren't well off so his wife dipped into the housekeeping money each week for about six months and presented him with a great new shirt for his birthday. He loved the shirt and put it on straight away. His wife was really pleased.
Later that day he decided to have a few beers with his mates at the local pub. As he left his wife suggested that he take off his new shirt in case he spilled something on it.
"No, no", he said, "I love this shirt and I want to show it off to the boys."
Anyway, the few beers turned into many and our birthday boy became falling-down drunk, so much so that he threw-up all over his new shirt. His mates cleaned him up as best they could, and when he sobered up a little he realised what his wife would say when he got home and she saw what he'd done to his new shirt.
"Oh no", he said, "my wife will kill me for spewing on my new shirt."
So his mates convinced him to go home with a $20 note in his hand and tell his wife that someone else had spewed on his new shirt, had apologised and given him the twenty to have it professionally cleaned.
So our hero arrives home and, as predicted, his wife hit the roof.
"Hold on", he says taking the money from his pocket, "I didn't spew on my new shirt. It was this other guy. He even gave me $20 to have it professionally cleaned."
His wife listens to his unlikely story and grabs the cash from him.
"There are two $20 notes here", she says. "What's the second one for?"
"Oh", he confidently replies, "that's from the guy who crapped in my underpants."