The innards of any animal: sweetbreads, liver, chitlins, fish eggs, pate, etc. And I'll go on record here that I have never tried any of these because the smell alone would stop me from three feet away.
But some that I've tried and promptly spit out include most green vegetables like brussel sprouts, green beans, kale, asparagas - anything that looks and tastes like grass, and not the fun kind, either.
Peas? Meh, maybe OK.
Most foreign foods. I'm OK with Chinese American, Italian American, and Mexican American foods, but I don't think I'd ever want to eat any Indian, African, Japanese, or any other food with any other country name in front of it. I don't know why - the food just don't look appetizing. I'm the American who would check out the McDonald's in every country I'd visit.