Canned fruit. As a kid in the 70's I went on field trips to the Dole plant and the Del Monte plant. Seeing rotten, wormy fruit going to the juicer, then that juice being put in the can with the fruit still makes it something I won't buy 50 years later.
Melted cheese, I don't eat grilled cheese sandwiches and I order my pizza without cheese as well. Nachos depends on how drunk I am. The texture is nasty to me.