At a clown convention in Mexico City, 700 clowns attempted to break the world record for laughter. They failed, probably because they turned and looked at each other, and the hellish scene of 700 cackling clowns scared them into silence.
They did manage to set Mexico's national record for continuous group laughter, though. Lest there be any confusion, the kind of clowns who convene in Mexico City for the International Clown Convention are the scariest ones around. Check out the guy shaking a limp, naked baby doll into the camera at 0:20.
[There was a video here]