You could never really find the funniest joke ever made, because people differ so much in their sense of humour. Just listen to two people talking about a stand-up comic, for instance - one will say 'He's really funny' and the other will say 'He's not funny at all'. What they really mean is that they each laugh at totally different things.

The idea of the funniest joke ever made is actually a joke in itself. It's a reference to an old sketch from Monty Python usually called 'The Funniest Joke in the World'. The idea of this sketch is that there is a joke so funny that anyone who hears or reads it will die of laughing. The joke is even developed into a weapon and used in World War II - you can see the whole 5 minute sketch here.

This is probably the nearest you can get to finding the world's funniest joke.