Man and his wife join a weight loss club. They're told to try and lose at least 2 pounds by the next week.

When they return after a week the mentor asks them how much they lost.

The wife begins, "I lost 10 pounds".

"That's amazing! Well done, and you?" He says, pointing at the husband.

"Well, I actually gained 10 pounds", the husband responds.

"Oh, that's no good at all. How did that happen?" asks the mentor.

"I bet my wife a tenner she wouldn't lose any weight this week".