Pits & Peeves
The food your character won't eat, the thing your character won't do…. Sometimes the negative is a great way of delineating something.
I once worked for a celebrated literary figure who enjoyed claiming he had never eaten an olive. Perhaps it was true. Regardless, it was comical because he had lived abroad for years and seemed so cosmopolitan. Whenever he came out with this tidbit – often at cocktails, apropos of the hors d'oeuvres — people would protest, No! It couldn't be true. Not even one, once, just in a martini? He stuck to his claim. It was yet another of many quirks that made him memorable and charming. If the food he wouldn't eat had been spinach or liver, some bitter thing commonly despised by children, I don't think it would have stuck in the mind so vividly. The example here is about a food a character doesn't like, but you could go a little wider. Is there something broadly agreed upon as fun (or indisputably normal) that your character despises?
PROMPT
Focus on an aversion – a food, a behavior, an object – that most would accept without special notice but which your character can't stand. Why this aversion?