Okay, it’s on my the tip of my tongue. I was watching interviews where they ask people what is their strongest point etc. If they’re asking about their weakness, the noun is ‘What is your Achilles heel?’ and when they’re asking about their best quality, they go, ‘What is your cup of tea?’
I’m looking for a word which means something you can’t stand, that annoys you. Usually interviewers ask them, ‘What is your ____?’ For example, the answer to that question is ‘Biting nails.’