Not being retarded.
I made the mistake of telling this joke to my then 8 year old nephew who retold it in my presence to his feebleminded great uncle. I was very uncomfortable when this happened, and my brother seemed to take great delight in this. "Hey Uncle Floyd! What's better than an Olympic Gold Medal?", asked the kid. "What?" replied Floyd. "Not being retarded!!" The kid laughed, so Floyd laughed, too. Nobody laughed more than my brother.
Leter I realized that neither the kid nor Floyd had a clue about the joke's meaning. And the kid's mangled version of the joke seemed to me to be even funnier for some reason. If I had to choose between an Olympic Gold Medal and not being retarded, I'd go with the latter. Who wouldn't?