Baloney is the nastiest thing I ever tasted. I almost gagged. The smell is nasty too.
In 2nd place is some salad I had at Chevy's. The dressing was pretty disgusting. I think they used some oil patch mixed with dirty water they found in the street and used it on my salad. That's how it tasted to me.
Oysters and clams. And sometimes other sea foods, but surprisingly not fish. For some odd reason it just doesn't turn my stomach like those weird, liquidy things that you're told to eat but it's really drinking them, and you can feel them going all the way down... slimy.