Dinosaurs - Season 1 Episode 3 -

Earl is excited to throw his mother-in-law Ethyl into the tar pits on her 72nd birthday, an old dinosaur tradition. The tradition specifies that men have the honor (and pleasure) of throwing their mother-in-law off a cliff. The day before the hurling, however, Robbie decides that it is the tradition and not his grandmother that should be hurled.