Ooh! I love answering this question!! :D

At first I made that fear as a sort of joke or character quirk for him, but then it became an actual part of him. I've come up with a few scenarios that might explain his irrational fear of jellybeans, but my favorite idea that I came up with was that he probably spilled a whole bunch of them in his bed somehow when he was a child, and then for the next few weeks he just kept seeing jellybeans everywhere. From that moment forward, he never wanted to see another jellybean. (It's still a work in progress! Haha)