Unfair Bet

Listen up, you smooth-brained goof, the joke is funny because you, the author, made a bet with a disabled kid in a wheelchair. He, thinking he had a chance, agreed to chase you for 1000 dollars, but you used the fact that he was in a wheelchair to your advantage to go upstairs. You did not play fair and thought you were being clever, but it was obvious from the get-go that it wasn't going to work in his favor. It’s cruel, but hey, you're not very smart, so you probably don't get that part.