With puffer fish, it will be just once. Seeing as how they're lethally toxic unless prepared just right, and even then they're still dangerous.
I can't stand any aquatic animal. They all have this same... fish, taste. Including things that aren't fish, like shrimp, lobsters, etc. I can tolerate small amounts of lobster and the like before I start getting nauseous, but any other aquatic animal leaves me wanting to retch.
I also don't particularly like anything with most vegetables, though some things I can still choke down.
Liver or tongue. Not because they taste bad, or because the concept grosses me out (neither of which are true), but because they're bland, and possessed of a horrid grainy texture.
Venison, because it's dry and tasteless.
Most ham, because it's bland and has an unnerving texture, in the same vein as liver or tongue.
Most steak, because thick veins of chewy fat and chunks of bone don't belong in prepared food, and having to sit and cut off a third of the meat on the plate because its inedible is obnoxious as hell. In the case of steaks that lack the above, there's no problem.
Ketchup, because vaguely tomato flavored corn syrup is a crime against civilization.
Mild hot sauces, because hot sauce should leave your whole face burning.
If we extend the category of "food" to cover drinks:
Wine. Because booze should not taste like rotting fruit doused in sugar.
Alcopops. Because booze should not taste like a used energy drink enema.
Pale beers. Because booze should not taste like watered down bread.
Flavored liquor. Because liquor should not taste like nyquil.