Comedy evolves. We long ago bid adieu to the physical acrobatics of Buster Keaton, the wisecracks of Bob Hope, the witty repartee of Cary Grant and Irene Dunne. The now-reigning comedy of embarrassment, seen in the films of Judd Apatow and the Farrelly Brothers and all the loss-of-virginity farces, seems particularly appealing to younger viewers