The strange thing here is that Marty McFly is using the slang “heavy” and Doc Brown doesn’t understand it. Yet the use of heavy to mean “profound, serious” started in Jazz in 1937. So Doc would have grown up with the word, and by the 80’s I wonder if it was really all that popular anymore. McFly is using 50’s slang in the '50s but the guy from the '50s doesn’t get the slang. Maybe because he’s not hip.
Propaganda is when you punch someone in the face and then quote them saying “I’ll kill you” instead of mentioning the face punch.