When Marty McFly accidentally travels back in time to the world of his parents' adolescence in 1955, the subtext is that he's entered a less complicated era of history. His father George is a smart, timid nerd who is invisible to his mother, a vivacious and popular beauty named Lorraine. Amidst this world of soda fountains and T-birds, is a two-dimensional view of the bully-victim relationship, as if children of the 1950s didn't have complicated antagonistic entanglements.
George is terrorized by a dumb, drooling brute named Biff and does his bully's homework in exchange for not being punched. In the film's denouement, Biff tries to force himself on Lorraine in the parking lot of a school dance. George grows so angry at the sight of Lorraine's suffering that he finally finds the strength to punch his bully in the face. This punch somehow ends the bullying and, when we see Biff and George as adults in 1985, they have a friendly relationship in which Biff even works for George. The message is an appropriately old-fashioned one: stand up to the bully and he'll go away.