I had a bad mussel once as a kid. Liked them before that, now I can't even look at them.
Okra- slimy nasty sticky. Reminds me of that green slime on ghostbusters. ewwwww.
My personal demon is tomato soup. I refused to eat it once as a child and my mother poured it down my shirt. I can't be in the same room with it now. And I love all other tomato based foods, raw or cooked.