Sailing on a friend's boat in Ireland 3 years ago, we came into a port that had a huge fish market along the quay. There was a great choice of fish available, and my friend went shopping and I was disappointed to see him come back with a big bag of mussels.
He saw the disappointment in my face. He said, you're not allergic to them? I said, I don't think so. I think I just don't like them. Well, he said, if you don't know you're not allergic to them, you can't have tried them, or you'd know. Thinking he had a point, I overcame my reluctance and we ate half the bag each. 15 minutes later I was on the deck, heaving over the side.
In a quiet spell, I heard him talking to his wife on the phone. I heard her shout, of course he's allergic to them. He asked how she knew, and she told him that when they had sailed to Portugal 2-3 year previously and anchored alongside me, he had given me a tin of mussels then. Same reluctance to try them, same reaction.
