Rationally or otherwise? Some of mine were:
Seeing a toilet with the seat up - it looked like an open-mouthed monster, and I remember it being at my eye level too.
Shoes with buckles, especially when someone else was fastening them on to my feet, because I couldn't get them off myself. Velcro ones were OK though.
Lifts, especially the old-fashioned ones with metal gates instead of sliding doors, now quite rare.
Balloons. Even now they bring me out in a cold sweat, because they might burst.