 After Clark Griswold (Chevy Chase (qv)) unsuccessfully attempts to  demonstrate his handiwork with the house Christmas lights to his  family, he asks his son, Rusty (Johnny Galecki (qv)), to help him  check all the light bulbs again. Rusty looks at his bare wrist,  pretending to have a watch, and excuses himself. Looking at a bare  wrist and pretending to have a watch is one of Chevy Chases  trademark gags.