THE MEANING OF PROPRIETY: 1972’s “What’s Up, Doc?” may be one of the funniest movies ever made. It’s a classical screwball comedy, with all the gags you’d expect from a film like this one and all of them visible, and it’s peopled with a large and expensive collection of stars, including Barbra Streisand, Ryan O’Neal, and Madeline Kahn (in her motion picture debut); all at the top of their game. It has a plot so unlikely and straightforward that we can't believe it for much more than 15 seconds a