The trap that got me the most is the mammoth skull bash. The logs also give me a heart attack but the mammoth skull makes me immediately ready spells every single time. I shake my head and laugh afterwards. I don't know what it is but spikes, doors and such don't bother me that much.

Most underground sections and the Dwemer ruins also creep me out. Because of the constant clanking and steam hissing you usually don't notice what's coming.

Biggest poop in tha pants moments was in a Dwemer ruin where I had to open a huge door by removing debris stuck in gears. The door finally opened so I scamper happily up the ramp towards it and lo and behold what comes out of the darkened passage behind it? A Steam Centurion O_o
Being a level 6 mage I ran until my pointy ears were flat from wind erosion.

I have the bad luck of walking into every single trap in a dungeon. They always startle me.