Beam Me Up, Scotty!: An unusual instance. While Heston does actually yell "Soylent Green is people!" during the film's climax, most people get the context wrong and believe that he screams it while running down the street and fleeing from the police. In actual fact he says it to the police, in the middle of a cathedral that has been converted into a homeless shelter, while being carried away on a stretcher. The "running down the street" scenario was actually from a Saturday Night Live parody of the film. They may also be getting it confused with the ending of Invasion of the Body Snatchers.
Defictionalization: You can actually find Soylent Green crackers out there, though it's not really made of people. (Or so we hope...)