Spoofed in Slam Dunk Ernest, when the title character walks into his friends' locker room and attempts to use urban slang to gain rapport with the African-American basketball players. His attempt backfires when he says, "Right arm. Out of state. Frozen." These malapropisms for "Right on," "Out of sight," and "Cool," are not well received by the other players.
This is part of the plot in the first Scooby-Doo movie: the gang starts getting suspicious when those who arrive at the island resort speak like any average teenager, while those who leave speak using awful Totally Radical slang. It's because they're actually monsters wearing a human skin, and Scrappy Doo taught them how to speak like "normal teenagers."
The movie Gleaming the Cube is named after a particularly interesting-sounding skateboarding term one of the writers overheard from a crew member's son. The boy had made the phrase up on the spot.
The Jets in the stage/film musical West Side Story speak (and sing) in a street language that Arthur Laurents made up, but includes actual Fifties slang and words.
Diablo Cody's films Juno and Jennifers Body include high school students using a lot of slang that Cody made up herself, such as "Honest to blog." Audiences are generally divided on whether it's an example of this trope or a clever way of side-stepping it.
This was outdated ASL slang from the '90s. She made a W, E (looking-ish thing), M, and L on her forehead.
In Better Off Dead, there is a scene where the teenage protagonist's father attempts to connect with his son while awkwardly using slang he is reading from a book on how to communicate with teenagers. He still gets some of it wrong, saying things like "Right off!"
Who can forget the immortal scene from FernGully: The Last Rainforest? We still have no idea if it was meant to be a satire (note Crysta's reaction) or if the writers were serious:
Zack: You know — bodacious, bad, tubular...
Zack looks meaningfully into Crysta's eyes
Zack: As in, you are one bodacious babe.
It was probably something resembling satire; when it becomes clear to everyone that Zack is making sense only to himself — and that his exaggerated surfer dude persona prevents him from reverting to normal English to explain just what the hell he thinks he's talking about — Batty quips, "Awesome use of the language, dude."
Made even more ridiculous by the fact that Zack is an Australian using early-'90s American surfer lingo. Though it's hard to tell he's Australian, since his voice actor is Not Even Bothering with the Accent.
Spoofed in Shrek the Third, where Shrek spews out a string of hip-hop slang in a failed attempt to relate to Artie.
Artie: Help! I've been kidnapped by a monster that's trying to relate to me!
In the movie Disturbing Behavior, Katie Holmes' character uses the term "razor" as analogous to "cool" or "sweet".
The Neverending Story III was just... ugh. Definitely only one of the many problems with this film (the primary being its existence) we had school bullies being referred to, by the other students, as "The Nasties", and Bastian's step-sister referred to his sense of style as being "Un".
Bill and Ted's Excellent Adventure seems to intentionally embrace this. Much of the comedy comes from the two characters' flamboyantly silly version of California teen slang, which turns out to have swept the world in a utopic future. Their legacy includes two prime directives: "Be excellent to each other," and "Party on, dudes!"
In Freaky Friday (2003), not only the dialogue, but the themes of the movie seem Totally Radical, adjacent to Adults Are Useless. The conversation in the restaurant where Anna (in the body of Tess, her mother) is talking with Jake over contemporary music (like they have a college degree in it) and then singing along with a rock cover "Baby One More Time" comes off as Totally Radical. The moral of the story seems to be that teenagers just need to be left alone, and not relate to their parents (or vice versa), because neither can understand each other.
A common complaint critics leveled at Steven Spielberg's Hook was that it invoked this trope with its approach to the Lost Boys, who ride around on skateboards, play basketball, and refer to Peter Pan as 'The Pan'. ('Pan the Man' at one point.) Their Catchphrase, "Bangarang" is intentional fantasy, but still comes across as outdated.
Dogma parodies this with "Buddy Christ", a figure that the Catholic Church uses to convert young people who are turned off by the depressing nature of Catholic teachings.
Mean Creek for the most part is a pretty strong aversion of this trope, the teen talk is realistic and full of realistic profanity instead of cheesy slang, things like drinking, smoking and marijuana use are straight up addressed, and the Truth or Dare game in it isn't your standard fiction one with only mildly embarrassing PG-rated aspects. However writer/director Jacob Aaron Estes did fail to realize that the teens of 2004 don't have the exact same interests teens in his day did, and don't consider Super Soakers the best thing since sliced bread or fantasize about Heather Locklear. Throwing your backpack in your direction only to pick it up and throw it again also seems more like a 90's thing than something common today.
Regina: Gretchen, stop trying to make fetch happen! It's not going to happen!
Used deliberately in Ferris Buellers Day Off. The secretary Grace tells the principal "The sportos, the motorheads, geeks, sluts, bloods, wastoids, dweebies, dickheads — they all adore him. They think he's a righteous dude" in regard to Ferris.
Inverted in Prince Caspian. They really, really tried to make the 1940s settings for the Earth scenes perfect and detailed... and then had the boys say "got it sorted," which is at least forty years ahead of their time. Twice. At dramatically important moments.
Though not an English-speaking example, the dialogue in the Norwegian war movie Max Manus also suffer under this trope, with actors who are supposed to live in World War II unwittingly talk like the nineties.
Disney's movie "Now You See It..." is full of this. The mains characters use phrases like 'a snowball's chance in you-know-what' and Danny talks like a ten year old girl at times.
Amy Heckerling, director of Clueless, invented her own Valley Girl inspired slang to prevent this.
The Smurfs: The Movie: Papa Smurf wearing Wayfarer sunglasses on the poster? Check. Smurfette turned into a shopaholic ditz right out of Sex and the City? Check. Smurfs rapping? Kill us.
Used to orient us into the '50s setting in Stand by Me, where Vern is so excited by news of a dead body in the woods that he can only say the now-ridiculous "This is so boss!" half a dozen times before explaining anything to the others.
The ABC Family TV movie Cyberbully suffers from this, with the teenage characters using terms like "bling" and "the clap". This movie was released in 2011.
Perhaps the strangest version of this is done deliberately in the 2006 film Brick. It is set in a modern day high school with teens and young adults but every character talks and acts like They are in a 1940s noir film, complete with hard-boiled slang and verbal tics that would sound like complete nonsense to modern teenagers (Or anyone else born after 1934). Needless to say, this adds immensely to the film's quality.
Pastor Skip from Saved! knocks himself out trying to relate to his students.
Bringing Down the House attempted to avert this. The movie uses a lot of hip-hop slang, so instead of using real slang and risk dating the movie or invoking this trope, they just made up their own slang instead.
Yello Dyno of Tricky People. So dated is his radicalness that he makes pop-culture references to Ethel Merman and Al Jolson.