Joan Rivers was on last night's Late Show with David Letterman, because The Great Joan Rivers Moment-Having of 2014 is not yet over. Letterman challenged her with questions that in other circumstances she might deem "negative," but she answered his with humor and whatever the Rivers equivalent of grace is, as she already has a punching bag in the form of CNN's Fredericka Whitfield, whom she now infamously jilted during a recent interview.