I have two.
Second favourite: at Uni, a very pretentious bloke was holding forth about how Prefab Sprout (remember them?) were the best band ever (better than the Stones, better than the Beatles etc.), mainly because of the depth and intelligence of their lyrics. One of the girls we were with just fixed him with a withering look and said "Oh yes, their lyrics...hot dog, jumping frog, Alberquerque." He shut up after that.
But my best has to be one of my friends from Uni - he's gay, and extremely camp, so has a natural advantage in the put down department. We were at a party one night, a few years after graduation, and the most boring bloke ever was monopolising the conversation with a monologue on his Very Important job as a Museum Curator. He had gone on and on about the importance of preserving history, the work on restoring artefacts, blah blah blah, and as he paused to draw breath my friend said, in the campest and most cutting drawl, "darling, really it's just dusting a load of old knick-knacks, isn't it?"
More please - I am in dire need of a laugh this morning.