Contrails (Chemtrails), submitted by Abraham. Ok, this kind of website is pretty much old news by now. We've all seen tons of sites going on about ufos and new world orders and, like this one, suspicious TRAILS of CHEMICALS! in our skies. So it's easy to skim one without thinking about it.
But seriously, take this moment to think about it. This guy is afraid of clouds. Clouds. Water vapor in the sky. Here let me illustrate my point with a photo:
OH GOD LOOK AT THAT CONDENSATION ABOVE US WE'RE DOOMED
Next up on my list of fears: air. After that: existing. After that: I don't know, clowns?