Ax-Crazy: When going over the government files on "marahuana," they talk about a teenager who became addicted to the drug and killed his family with an ax for some reason. It might have been an allusion to an actual person who was believed to have murdered his family while stoned (he was schizophrenic).
It might not have been the best idea to start the film by giving detailed instructions on how to make and even smuggle joints.
Cool Car: The main teen characters have a then-brand-new Ford convertible sedan. Ironically, the use of Stock Footage means the police cars shown are 5-8 years old (the equivalent of a 15-20 year old car today).
Epic Fail: This movie's message is that Drugs Are Bad. It is impossible to take it seriously because of how over-the-top it is.
Even Evil Has Standards: Mae the drug moll doesn't like selling pot to teenagers, a qualm her partner Jack doesn't share.
Ralph, whose near-rape of Mary leads to her death, is the only one of the gang who shows any remorse that Bill is convicted of her murder. Though it is implied that his attitude is primarily a side effect of marihuana usage.
Frame-Up: They try to frame Bill for Mary's death.
Framing Device: Dr. Carroll, the high school principal, relates the film's events while addressing a PTA meeting about the scourge of marihuana.
Karma Houdini: Jimmy runs a man over with his car while stoned and gets away clean. Odd for a 1930s movie (since The Hays Code had a rule about bad people not being able to get away with committing crimes) and especially odd for this movie.
Although we see Mae being grilled by the cops, we never hear what punishment is eventually dished out to her (possibly because of her attitude toward underage clients).
Karmic Rape: This happens in the musical number "Little Mary Sunshine," in which Ralph's marijuana-facilitated attempted seduction of Mary goes horribly, horribly wrong.
Leave the Camera Running: There seem to be a lot of long, pointless shots in the movie, such as Bill dropping his book, picking it up, and dusting it off.
Lost Aesop: Invoked, for cripes sake! The lead jurist won't accept one juror's "reasonable doubt" argument, but then he envisions a hanging noose, reminding him that a man's life hangs in the balance. He then proceeds to deliberately ignore his own epiphany and continues bullying the jury with his viewpoint.
Marijuana Is LSD: Even less accurate, marihuana's shown as a violent narcotic. Hell, some of the posters for the film were covered with needles.
Miscarriage of Justice: Bill is found guilty of Mary's murder even though he was framed, but it's averted at the last minute when Blanche admits that it was actually Jack's fault.
The Musical: The original film was later made into a highly popular stage musical in the late 90's, and then that was made into an award-winning Showtime movie in 2005.
Nerf Arm: seriously, someone was killed with a curtain rod?
Sliding Scale of Shiny Versus Gritty: Very much on the shiny side, especially considering the producers' intent. The aforementioned nicest drug hangout in cinematic history and new car and all the young drug users are well- (and one would presume by 1936 standards fashionably-) dressed.
Smoking Is Cool: Averted. This was one of the first attempts (if not the first) at making smoking look uncool, and viewers might have a hard time believing they didn't set the studio on fire... Using "joints" which look exactly like factory-produced cigarettes is a contributing factor. On the other hand, it's notable that the two leads, Bill and Mary, are depicted as incredibly square even for 1930s standards — "Gee, hot chocolate! — and yet are shown to smoke (regular tobacco) even before they get introduced to pot.