All Just A Day Dream: After Micheal gets shot in the head at the climax, it turns out the films animated sequences were all in his head as the film switches to a real life Micheal for the last several minutes. And given it happens after Micheal loses a game of pinball (a recurring symbolism piece) and how closely his real life parallels that of the cartoon fantasy, and not to mention the films POV driven nature was constantly foreshadowed throughout the film (with the frequent mixing of animation and live action, and film literally starting with a real life Micheal playing the pinball game) this twist actually comes off as very well thought out.
Art Shift: Only happens two times. The scenes that go into underground comic book form, and the live-action at the ending climax of the film.
Ax-Crazy / Mama Bear: Ida, Michael's Jewish mother, who is really over zealous about keeping him out of the influence of Angelo / Angie, his Italian Catholic father, who is part of the mafia and frequently cheats on her. She even tries—and fails—to stop Shorty from killing her son.
The Big Rotten Apple: Micheal lives in New York, which is presented as being very run down, seedy and run by The Mafia. Ironically, Micheal draws his inspiration directly from this environment.
Being Personal Isn't Professional: The reason why the Mafia refuses to honor Angie's request to off Micheal, citing his reasons as being personal and not business related. Given how much Bakshi despises the Mafia, this is obviously meant to be a satire on the fickle "honor" system used by them.
Death by Cameo: A caricature of Ralph gets killed off by Michael during a racket in the movie.
Deranged Animation: The whole film is a surreal fantasy loaded with metaphors and symbolism and a load of topical and biographical undertones. And besides the rugged and sometimes bizarre designs, the animation really does get pretty crazy, especially the scene where Micheal gets shot, and it's nightmarish aftermath.
Fan Disservice: There is a common Running Gag in the film involving older or repulsive women's breasts falling out of their shirts, which they promptly snap back in.
Fictional Pinball Game: Michael repeatedly plays a pinball game throughout the movie, in a metaphor for the randomness of existence.
Gainax Ending / Bittersweet Ending: The film ends with Micheal getting shot in the head by Shorty, which leads to a nightmarish death sequence...and then the film switches to the real life Micheal, who, after losing a game of pinball, storms off and then meets up with the real life Carole, dancing her with in the park after bickering with her. The end.
Generation Xerox: Micheal ends up going down a path of crime not unlike his mafioso father, but he doesn't last long in it due to his dad ordering a hit on Micheal for dating Carole.
George Jetson Job Security: It's clear that Carole, with her stubborn, no nonsense attitude, just can't hold a job. She quits her first job as a bartender right after bickering with her boss over Shorty initiating a bar brawl, and gets fired from her second job shortly after starting it by flashing her gams at an old man (which gave him a heart attack). She and Micheal eventually turn to forming a racket so they can make enough money to move out to California. And after the films ending switches to real life, we find out the real Carole has no luck holding a job either.
Grey and Gray Morality: There are no real heroes or villains in this story, and few if any of the characters are truly sympathetic—all of them are messed up in some form or another, be it physically or mentally, and have their own personal agendas to carry out.
Green-Eyed Monster: Shorty hates Micheal for Carole preferring a relationship with him over himself (as Carole clearly finds Shorty unpleasant to be around). This makes Shorty more than willing to carry out Angie's hit on Micheal at the end.
Handicapped Badass: Shorty, a man who is literally missing half of his body, but is quite fast on his wooden cart and, given his profession as a bouncer, will kick your ass with his own bare hands.
I Have No Son: Angie, Micheal's racist father, tries to get the Mafia to put out a hit on Micheal for "disgracing the family" by dating Carole, a black woman. The mafia refuses on the grounds that the hit is personal and not business related, but then Angie meets up with Carole's devoted bouncer Shorty, who is jealous of Carole dating Micheal and is more than willing to deliver the hit, which he successfully carries through.
Irony: Angie, Micheal's dad, is definetely against his son dating Carole, enough to try and order a hit on him for it. It turms out he was right to be suspicious of her, but for an entirely different reason than his racism when Carole drags Micheal into running a crime racket together. And just when Micheal starts going down a path of crime like his mafia dad before him, Shorty comes along to pull off the hit on the now corrupt Micheal.
Jerk Ass: As mentioned above, most of the characters are very callous in personality.
Karmic Death: Shortly after starting a racket with Carole and willingly murdering a man for money, Micheal gets shot in the head by his dad's new hitman. Shorty. Of course, it turns out it's literally all in his head.
Meaningful Name: The title of the film; the "Heavy" is the dilemmas of life, and the "Traffic" is the people who experience it.
Shorty for Carole's bouncer, a man missing half of his body and moves via a wooden cart with his own arms.
Nighthawks Shot : The painting is homaged in a brief scene late in the film.
Offing the Offspring: Angie tries to do this twice in the film. First, he tries and fails to get the Mafia to put a hit on Micheal, and the second time, he enlists the aid of Shorty to pull the hit, and he succeeds.
Panty Shot: Carole pulls one on purpose during a gig as a Taxi driver, and to an old man, who literally has a heart attack from the sight, which predictably costs Carole her job.
Rage Quit: When the final part of the film switches to live action, Micheal smashes apart a pinball machine that he lost at, and storms off.
Roger Rabbit Effect: Some of the scenes in this movie have animated characters over live-action backgrounds; a part has human girls in the backgrounds. However, most of the live action doesn't directly interact with, but compliments the animation.
Shout-Out: The loosely drawn comic art seen in parts of the film (notably the "Maybellene" segment) is an homage to the art style of pioneering cartoonists Otto Messmer and George Herriman.
After Carole briefly walks out on him, Micheal jokingly remarks "Mick Jagger, I'm not."
Micheal, when posing as Carole's manager, refers to her as "the fourth Andrews Sister", saying they kept her in the background because she was black.
Stealth Pun: In the films ending, Micheal gets shot in the head by Shorty, and after the nightmarish death sequence, snaps back to reality in a pinball arcade. In other words, the whole film was "All in his head."
Stripperific: Carole is very skimpily dressed from the waist up.
Symbolism: The recurring pinball machine Micheal plays is meant to be symbolic of fate and peoples place in the universe, per word of Ralph; that once you step outside, anything can happen, and the only influence you have over the universe is the flippers. Sometimes you make it big and get the high score, other times you have to put another quarter in.
The Worlds Oldest Profession: Carole poses as a prostitute in order to set up a businessman for Micheal to kill, so they can both make off with his money.
Toxic Friend Influence: Carole, with her uncompromising, hardheaded attitude towards her goals, eventually drives Micheal along with her into a life of crime to making the money so they can both move to California, even resorting to murder for profit.
Underground Comics: Michael is an underground cartoonist. He even tries to get a job at a syndicate by pitching a story to it's elderly CEO, but he literally dies upon hearing Micheal's very bleak, satirical story idea.
Your Head Asplode: Micheal gets shot in the head by Shorty, and it is depicted in very gruesome detail, all filmed in slow motion. Then it turns out that's just an animated metaphor for Micheal losing a game of pinball in real life—and given the films recursive symbolism, losing a game of real life in general.