Butter or any type of spread in sandwiches?
If I make say a cheese and tomato sandwich/roll, I never spread the bread with butter/margarine as it literally makes me heave. I might spread on a bit of mayo if it seems dry but that's it. If I go to a cafe I ask for the spread to be left out. If I buy a supermarket sandwich I can only eat tuna mayo as for some reason the spread doesn't bother me and is usually invisible.
I'm not fussy in any other way and have never met anyone else with the same aversion.