I just thought of my actual fear...
Clowns. But don't write a book about that, it's been done.
But the other day my sister was driving and she passed a clown - and was so distracted that she'd slowed down after seeing this in her rear-view mirror - this INFURIATED the clown who then began driving very aggressively and was being totally scary to my sister
I think I would have soiled myself.