Quagmire's personality changes when he adopts a pet cat, which irks Peter. Meanwhile, after Brian gets arrested for having a bag of weed in his car (during Peter's botched attempt at ditching Quagmire's dead cat in the woods), he starts a campaign to have marijuana legalized.
"Episode 420" contains examples of:
- All for Nothing: Carter agrees to publish Brian's book in exchange for Brian completely changing his position on pot and making it illegal again. Brian does so, only for his book to be panned by every critic in America and not sell any copies.
- Are You Pondering What I'm Pondering?: When Lois catches Brian trying to use some of Stewie's urine to use in a random drug test orchestrated by Joe, Lois scolds Brian for going to such lengths and tells him that he has to make a change if he intends on doing so—and it's implied that Lois was going to tell Brian that he should just simply stop smoking marijuana.
- Arson, Murder, and Jaywalking: Brian says that with pot legalized, crime is down, productivity is up (which, according to DVD commentary, they couldn't say as the censors did not want marijuana to be glamorized), and ratings for Doctor Who are through the roof.
- Artistic License Law: Despite Brian convincing all of Quahog to support cannabis, that would not make it legal at a state level, which is what would need to happen for people in the town to be able to smoke it so openly. The town would most likely be able to decriminalize it.
- Bad "Bad Acting": Carter and Peter's anti-cannabis video features this from both of them.
- Black Comedy Animal Cruelty: Peter tries to shave Quagmire's new cat with a hand razor, but he ends up killing it.
- Blatant Lies: Urging Brian not to take Carter's deal, Stewie says his book is good enough to publish on his own (all while giving a very forced smile and unconvincing line).
- Humiliation Conga: Tom Tucker reports that Brian's book set a record as the worst selling novel of all time. Not even one copy was sold, due to the extensive panning from critics. To add further insult to it, Stewie builds a fort out of unsold books in the living room and refers to it as "a house made of mediocrity."
- Hypocritical Humor: Lois supports marijuana legalization and disapproves of Brian doing so despite having smoked pot herself. Brian even calls her out on it.
- Jerkass: Peter, who not only kills Quagmire's cat, but flatly states he killed the cat, grabs the reward money and closes the door on him before Quagmire has a chance to react.
- Kick the Son of a Bitch: Carter's goons viciously beat Peter in the same episode that Peter killed Quagmire's cat and tried to cover that up.
- Kindhearted Cat Lover: Quagmire to the point of irritating his friends with how much he fawns over his cat.
- No-Holds-Barred Beatdown: Peter is given one before and after getting into Carter's car for no other reason that Carter being a Jerkass
- Selective Enforcement: The cops blatantly ignore the fact that Peter has a small body bag in the backseat, along with a note saying "this is where we'll hide the body," and is not only covered head-to-toe in blood, but driving drunk, but when they discover Brian in possession of a quarter-ounce of pot, they arrest him on the spot and throw him in jail.
- Shoot the Shaggy Dog: In the end, pot is made illegal again and Brian's novel (which Carter promised to publish if pot was made illegal) ends up selling no copies whatsoever.
- Stoners Are Funny: As if the title's name wasn't enough.
- Take That!: Carter and Peter make an anti-cannabis video showing Adolf Hitler as a pot smoker, but are then sued by Fox News for using their copyrighted image of Hitler.
- At one point Peter is too stoned to properly setup his own cutaway, and thus it ends up simply being a Long List of celebrities he hates. Chris Martin gets mentioned four times. Other celebrities mentioned on the list include: Carlos Mencia, Amy Winehouse, Paul Tsongas, Andy Samberg, Justin Timberlake, Eve Plumb, David Arquette, that forehead guy on The Office (Rainn Wilson), and Kate Beckinsale. According to DVD commentary, the celebrities on that list were picked at random and the writers have nothing against them, though some of the celebrities on that list are considered annoying, detestable, marginally-talented, and/or overrated enough for viewers in real life to hate them.
- Technician vs. Performer: Crops up a little during Brian's original protest in the park. He is the technician, as he stands on a stage and loudly addresses the facts of the situation. Every single person there ignores him no matter how loudly he talks. Stewie serves as performer, suggesting doing a fun song to get people invested in his cause. Brian takes his advice, and it works.
- Title Drop:
- Parodied in a cutaway, as Peter loves it when movies do this.Jack Ryan: I'm telling you, these drug dealers represent a clear and present danger to the United States!
Peter: Ah! Ah! He said it! He said it!
Melvin Udall: All I'm saying is, what if this is as good as it gets?
Peter: Ah! Ah! There it is! There it is!
Superman: The only way for me to solve this crisis is to be Superman IV: The Quest for Peace.
Peter: So, that's why they called it that.
- Later, after Peter and Brian get stopped, the cops find Brian's pot and arrest him.Cop: I don't appreciate drug addicts in my town! I'm a family guy!
Peter: Ah-ah! Ah! He said it!
- Parodied in a cutaway, as Peter loves it when movies do this.
- To the Tune of...: "A Bag O' Weed" is sung to the tune of "Me Ol' Bamboo" from Chitty Chitty Bang Bang.