George Plimpton will try his hand at anything. First he played a bit part in a John Wayne Western. Then he chanced his arm on the flying trapeze at the circus. Now he tries the loneliest job in the world: stand-up comic. Alone on a stage in front of an audience, he has only his jokes between him and disaster. Bob Hope, Woody Allen and Buddy Hackett all have advice for Plimpton. Laugh-In's comedy writers provide the material. But on the big night at Caesar's Palace at Las Vegas he is out there alone in front of 1,200 people, an audience used to the best entertainment the world can provide.