Better Export for You: All but the German-export DVDs suffer from terrible Clumsy Copyright Censorship, with missing music and scenes; only the German release features the original music track and entire show.
Billing Displacement: Johnny Depp is billed first on the DVD. For much of the run, Holly Robinson (Peete) was probably a more prominent cast member than him (helped by the fact that she was the only cast member to stay for the entire run). In fact, for the fifth season DVD sets go so far as to have Depp as the main focus on the cover despite the fact that he only appears in one episode, and it's leftover from season 4!
California Doubling: Though supposedly set in the U.S., the fact that 21 Jump Street is shot in Canada is made clear by the fact that the extras were hired locally and thus do decidedly non-US things like say "grade 3" instead of "3rd grade" and write graffiti with words ending in "-our" instead of "-or". The only slightly blurred "Beautiful British Columbia" license plates are also a dead giveaway. Though when a license plate is clearly visible, it says "Beautiful Evergreen State", which is the Washington state nickname, but with the British Columbia plate design. The characters also make mentions about Parker Center (then LAPD headquarters) and use California Penal Codes to describe crimes.
Dawson Casting: Subverted. The main characters are clearly identified as adults, but they are assigned to this undercover unit because they all look young enough to pass as teens, though many of the non-cops play this trope straight.
Fake Nationality: Ioki's character was originally written as Japanese, while the actor was Vietnamese. This was retconned to make the character a Vietnamese person as well, who had just been pretending to be Japanese.
Missing Episode: The "Blackout"' / "Business As Usual" episode is the last episode of Season 4, but isn't included on Season 4 DVD sets. It instead is on the Season 5 DVD set. Some more cynical fans think this was done to use Johnny Depp's popularity to sell more Season 5 DVDs—Johnny Depp appeared in Seasons 1-4 but not in 5, and this episode in question is his last one.
The Other Marty: Originally, Johnny Depp turned down the role of Tom Hanson, and actor Jeff Yagher was cast in the role and the pilot was shot using Yagher as Tom Hanson. Then the producers decided to let go of Yagher, and use Johnny Depp instead.
Out of Order: "Blackout" (to add further to the confusion, this episode is a.k.a. "Business As Usual") is (in airing/numbering order) the last episode (26) of Season 4 and the last episode character Hanson appears in—his character is next Chuck Cunninghammed out of existence without any set-up. Taking a look at the last episodes of Season 4 though, it becomes clear that episode 20, "Last Chance High", actually subtly set up his character leaving—during it, he discusses with Penhall stuff like "Aren't we getting too old for this?", "We should move on", and "[Their gag] the McQuaid brothers are dead, finito!". The episode then ends with Penhall agreeing they've grown out of this phase, and giving Hanson a big man-hug. This clearly was to be the last episode character Hanson was supposed to appear in. The "Blackout" episode apparently was pushed back to the end of the Season because it was deemed controversial (dealing with high school students physically attacking their teachers at school), which explains why it is such a weird ending for the Season.
Playing Against Type: Many watchers of the episode "The Education of Terry Carver" got a hell of a shock when Jonathon Crombie (who at the time, and right up until Anne with an E came out decades later, was the definitive image for the one and only Gilbert Blythe) suddenly pulled a knife and raped the title character.
The Season 4 episode "Old Haunts in the New Age" seemed this to Season 1 episode "Worst Night of Your Life". Both are Halloween episodes; are about arson in schools; feature a character that at first seems to clearly be the offender but isn't note In Season 1, the girl that broke into school to get a tape back, and is arrested; in Season 4, the girl that had psychic visions of fires to come; in both, the police officers reveal their true identity pretty quickly to these respective previous suspects and then go on to work together with them to get the real arsonist; in both, religion or spirituality played a role (the 1st took place in a Catholic school, the 2nd was about spiritualism); both ended with the police officers attending a Halloween prom undercover; and a fire breaking out at that prom despite the efforts of police and the schools to prevent this; and the fire doing no physical damage to anyone, but revealing the real arsonist at the prom, who then got arrested.
There were two episodes ("Afterschool Special" and "Say It Ain't So, Pete") that featured Fuller going undercover as a teacher, quickly figuring out a student was illiterate, and convincing the student to learn how to read.
Referenced by...: The show is referenced in Doug, as Doug Funnie's home address is 21 Jumbo Street, an amalgam of both the show title and the production company behind the show, Jumbo Pictures.
Science Marches On: In Season 2's "Big Disease With a Little Name", Hanson goes undercover as a bodyguard to a teen with Aids; in Season 5's "The Girl Next Door", McCann goes undercover to investigate a hit-and-run of a teen who turned out to be HIV positive; it turns out that he'd infected his female friends-with-benefits with the virus as well, which was the motive. Not only does the show now distinguish between Aids and HIV positive (which didn't often happen at the start of the epidemic), but the Season 5 episode acknowledges the advancements in treatment; the teen in Season 2 dies a fairly short time after being diagnosed, but in Season 5 a HIV positive character is taking AZT, and ends the episode by getting into a drug trial that might extend her life even further.
Throw It In!: The tattoo Hanson gets on his arm in "Fear and Loathing with Russell Buckins" is the actual tattoo his actor Johnny Depp already had (an American Indian Chief, in tribute to his part-Cherokee heritage).
You Look Familiar: MANY actors were "recycled" for different guest roles. Some examples:
Jason Priestly (of later Beverly Hills 90210 fame) played a troubled teen in "Mean Streets and Pastel Houses" and later played a different character in "Two For the Road".
Lochlyn Munro played different characters in multiple episodes.
One actor, Don S. Davis, even appeared no less than 6 times in different roles, including twice as (different) high school principals, and once as a prison warden.
And another, Jay Brazeau, appeared 7 times though he was a judge twice and was unnamed on one of those occasions. It was likely the same character.
Career Resurrection: Ice Cube seems to have found his niche as a comedic angry black man after a string of flops and unremarkable films.
Corpsing: You can hear Rob Riggle (Coach Walters) crack up when Schmidt uses his track baton as a penis while he's holding it.
Dawson Casting: Although the movie parodies this with Jonah Hill (29) and Channing Tatum (32) trying to pass for high school students, it's still played straight with the actors playing the actual high school students. Brie Larson was 22 and Dave Franco was 27, both playing 18-year-olds.
Distanced from Current Events: In the DVD Commentary, it is mentioned that the line "Doing cocaine with Willie Nelson's horse" was originally "Doing cocaine with Whitney Houston's niece." This was changed because of Houston's death shortly before the editing of the movie was supposed to be finished, and at the last minute they had to call the actor to come in and dub over a new line.
Dyeing for Your Art: Jonah Hill actually lost forty pounds for the movie, in order to be able to do some of the more physically demanding stunts.
Killed by Request: Johnny Depp accepted to reprise the role of Tom Hanson at the condition of killing the character.
The directors of these films are best known for Cloudy with a Chance of Meatballs and The LEGO Movie. Lampshaded by a TV spot for The LEGO Movie, which played up that it was from the directors of 21 Jump Street and 22 Jump Street, then adding, "Neither of which have anything to do with this movie."
At the time Channing Tatum was pretty solidly typecast as an action star or romantic lead. This marked his first big comedy and, along with Magic Mike, showed that he had quite a flair for it.
"Take That!" Tit-for-Tat: Jenko cursing Glee was most likely in response to the show's first Christmas episode having a character ask Santa for "Channing Tatum to stop being in stuff."
Throw It In!: Ice Cube improvised many of his lines.
While appearing on The Howard Stern Show, J. K. Simmons revealed that he was considered for Deputy Chief Hardy, but scheduling conflicts prevented him from being cast. Simmons said upon seeing the movie, that this role was one of the few he would like to have played for the comedy.
