Weirdest one I ever heard of, and one I'd never be able to survive with (since peanut butter is one of my reasons for living):
Arachibutyrophobia- fear of having peanut butter stick to the roof of your mouth.
I developed two fears in my youth out of circumstance that I wasn't born with. First, clowns. My parents were watching that terribly cheesy It miniseries when I was, what, five? And I sneaked into the room and hid behind the couch during the opening sequence with the killer clown. Since then, I have been rather creeped out by them. To the point where when a coworker came dressed as a clown on Halloween this past October, I started shaking and sweating, and our boss had to tell her to take her wig and mask off so that I could function. I have absolutely no desire to go to the circus any longer, and the close affiliation they have with clowns makes me feel a little uncomfortable when I see them on TV. Actually, I'm kind of afraid of the movie Dumbo now. Especially the scenes with the clowns, go figure. I'm fine with mimes, though- they don't scare me, they just annoy the living crap out of me.
Second, heights. This is okay, since I'm short, but I wasn't born afraid. I grew up in Las Vegas and was at the top of what was then the Stupak tower (now called the Stratosphere)- it closely resembles the Space Needle in Seattle and is basically the same thing, a huge tower you go to the top of to observe and do the little activities on (like paying ten bucks for a goddamn hot dog...). I reiterate, it was new, only open for a few weeks, so they were still figuring out various kinks in their system. I went on the roller coaster, an electric one, with my sister, and suddenly it stopped in the middle of a semi-sideways pass that had us looking down at the Las Vegas Valley. Apparently, there had been a fire in the kitchen of one of the restaurants up there, and it caused an electrical shortage resulting in the ride to stop. We were trapped for two-and-a-half hours. I dreamed of falling off a cliff that night. What's strange is that at first, I was okay- I could still climb onto the counter to get spices out of the cabinet or something, although with less confidence than before. But it has gotten much worse lately, to the point where I have to really steel myself if I want my thyme, and the sooner I get down, the better. I'm okay as long as I'm not paying too much attention at, say, a mall. And I'm fine going up stairs in houses (better if they're surrounded by walls). But if I let myself think about it, I get sweaty palms and my stomach lurches, especially if I have the dumbassity to look down.