In this scene from The Philadelphia Story, C.K. Dexter Haven (Cary Grant) and George Kittredge (John Howard) react at the first sight of a hungover Macaulay Connor (James Stewart; Oscar winner--get used to it Fonda fans) singing "Over the Rainbow" while carrying a hungover Tracy Lord (Katharine Hepburn) back home at dawn...on her wedding day(!). Not only is the above-shot priceless, so is the dialogue in the subsequent scene. As many times as I've seen the film, it was only recently that I noticed how good John Howard's reaction is here.
By the way, there have been some tremendous comments in the Katharine Hepburn: The Philadelphia Story (1940) entry! It's amazing how much fascinating insight can be read into this marvelous movie.