There are few feelings more satisfying than being able to prove your ability or expertise at something after being underestimated. For example, I always reveled in the look of shock and awe on a man's face when he thought he could out-drink me in college. Someone asked Reddit: "When did someone challenge you at something you were an expert at?"
1.) From MarkHirsbrunner:
By no means an expert (I'd probably rate in the 1500s), but I've played chess since I was a small child and was the best player in the middle school chess club. The guy who owned the pool hall me and my juvenile delinquent friends hung out in was talking about how dumb kids are these days and said he bet nobody in my group of hoodlums could play chess. I beat him soundly, then again in the rematch.