I'd say I'm equally triggered by most of the things humans fear, but my greatest reaction comes with falling. By this, I mean letting people win a debate over my life.
We see this everyday, and personal, it's just annoying. I hate it when people come up and say things not carrying any valid points about my life, my greatest fear comes in ever letting them have a chance to affirm their knowledge of me, perhaps with the phrase "I knew it", accompanied with the rest of the bullshits...