Clowns are scary. They attack you in your dreams and try to suck your blood. They're only good for one thing: making balloon animals. Besides, they must be evil: anyone who can take a long, phallic balloon and twist it into a weiner dog or a sword or a hat must be affiliated with the Devil in some way.
Okay, fine. I learned to make balloon animals a month or two ago. It's fun. I can make a weiner dog and a bunny. I'm not evil, but clowns are. I guess it's not the balloon animals that make them evil.