Syringes. I can calmly tell a doctor that a syringe scares me, and that though I will try to control myself, I will freak out. They never believe me, because I can talk about the irrational fear so rationally. As soon as the syringe comes out, I start crying, shaking, and freaking out.
Also, people standing behind me. If someone walks up and just stands behind me, I usually react violently. When someone actually moves to stay behind me when I turn, I get flight-or-fight responses, strong. That isn't so much a phobia as an echo of childhood trauma though.