A (usually) mundane and useless piece of knowledge, or field of expertise, that comes into profound effect as the one question you can answer at a pub/supper quiz.
It has also been known to be used as an excuse for quiz players with poor general knowledge.
Quiz master - 'What is the radius of the centre circle on a standard size soccer pitch?'
Person 1 - '9.15 metres'
Person 2 - 'How on earth did you know that?!?'
Person 1 - 'Oh it's my pub quiz question, don't expect answers to any other questions!'