Mine would have to be getting my feet/toes bitten off by large fish/sharks when I go swimming, Or when I walk over a storm drain and feel as though it's going to collapse from underneath me. How about you guys?
Spiders. I know it's a typical answer, but something inside of me just flips when I see them moving about near me. I'm not really afraid of anything else at all and I've tried really hard to get over my fear of arachnids, but whenever I try going near them, my body shakes and I sweat.
I think I might of had a bad experience in a past life with spiders... :P