A Clockwork Orange

In the future, a sadistic gang leader is imprisoned and volunteers for a conduct-aversion experiment, but it doesn't go as planned.

In an England of the future, Alex (Malcolm McDowell) and his "Droogs" spend their nights getting high at the Korova Milkbar before embarking on "a little of the old ultraviolence," while jauntily warbling "Singin' in the Rain."

After he's jailed for bludgeoning the Cat Lady to death, Alex submits to behavior modification technique to earn his freedom; he's conditioned to abhor violence. Returned to the world defenseless, Alex becomes the victim of his prior victims.