National Lampoon takes on another stereotype of middle America: the family vacation. Chevy Chase, his face pinkened by the strain of having to be in control, plays the affluent suburban patriarch who leads his family on a summer jaunt from Chicago to Disneyland (here rechristened Walleyworld). The result is not so much a comedy about American values as a 2,500 mile skid on a banana skin. The visual gags come thick and fast, and are about as subtly signposted as the exit markers on a freeway. An exercise in the comedy of humiliation which is the stuff of shamefaced giggles.