Oysters
I am a big seafood fan and could eat anything until a few years back I had a very bad reaction to oysters.
No anaphylactic shock just a violent bout of vomiting. Initially I put this down to a bad oyster but I have had a repeat of the incident and so regretfully I can't eat oysters. My experience is not unique as I have met a number of people who have reacted in this way to oysters.
I have no trouble and continue to enjoy all other types of seafood.