Ants. I hate ants.
When I was a kid, I fell asleep outside one time and woke up with hundreds or thousands of them crawling all over me. Never have liked the little bastards ever since and I semi-freak out if one is on me now.
TOTD: What is your secret terror where even the thought of it, while not necessarily harmful or fatal, just scares the living bejeebus out of you?