Woman: "If you were my husband, I'd poison your tea."
Churchill: "Madam, if you were my wife, I'd drink it!"

Woman (to a slightly inebriated and rather young Churchill): "Young man, I like neither your mustache nor your political opinions."
Churchill: "Madam, you are unlikely to come into contact with the one as with the other."

But my favourite story of Churchill's wit took place when Churchill was a very young Liberal Member of Parliament. At the time, the Liberals were the opposition and the Tory Postmaster General at the time was a man called Wilfrid Paling. Paling had been responsible for something of which Churchill disapproved, so Churchill got up in the House of Commons and told him so, with acid for sauce. So pungent were his words that Paling lost his temper, jumped to his feet, and shouted out "Churchill! You're a dirty dog!" Churchill merely looked over his glasses at him and replied "Take care, take care! You know what dirty dogs do to Palings!"