Spontaneity of wit can be over-valued, I think. The carefully crafted zinger, trotted out when the perfect occasion arises, gives a greater pleasure than the cleverest riposte thrown out on the moment. Oscar Wilde's greatest bon mot, though it appears nowhere in his writings and survives only through the reports of those who heard it, was obviously lovingly shaped in the privacy of his chambers, and held back by him until the moment was right. I refer, of course, to his immortal literary evaluation of one of Charles Dickens' most famous scenes: "One must have a heart of stone to read the death of Little Nell without laughing."
My old friend and Columbia Philosophy Department colleague Sidney Morgenbesser, now sadly departed, was the author of countless repeatable quips. One of my favorites, not all that well known, concerned the New York Jewish pompous, self-important, faux English literary critic, Lionel Trilling, who taught for many years at Columbia. Morgenbesser came upon him one evening at a social gathering where Trilling was, in his customary fashion, pontificating about something or other and trying as hard as he could to seem to be an Oxford Don. Sidney walked up to him and, in his loud, penetrating voice, said, "Ah, Lionel. Incognito, ergo sum, eh?"
Sidney published almost nothing in his life, but a line like that is worth a dozen academic journal articles.