A disco-inspired sequence in an otherwise unrelated work. Sometimes even featuring the full Standard Disco Equipment!
May be the doing of a Disco Dan, but such a character isn't even necessary to bring some Disco interlude out of nowhere.
Of course, this doesn't count if the show is set in The Seventies, or has Disco renewal as its main subject (like the 2008 French movie titled, guess what, Disco). This trope is for gratuitous Disco moments with little justification (in-story)... besides the Rule of Cool.
May be used for a Dance Party Ending. Most extreme cases can be Big Lipped Alligator Moments.
The anime features a scene in an early episode where Haré comes home to see Guu and Weda have set up a Disco in the house and are getting down with their bad selves. Guu's even sporting an afro, which Haré realizes is the village elder's lost chest hair. Weda actually greets him with "Welcome to the hippest trip!" ŕ la Soul Train.
And then, the second ending credits are Disco-themed.
The Bee Gees' "You Should Be Dancing" plays out before the end credits roll.
Animalympics has a musical number set at the "Noah's Ark Disco".
In The Lorax, Ted's mom demonstrates why fake trees are better than real trees by showing off her Oak-a-matic's disco setting. Later in the film, she's shown to have a mini mirror ball hanging from the rearview mirror of her car.
In The Naked Gun 33 1/3: The Final Insult, there is a flashback of the characters during the '70s in an appropriately Disco setting. Part of the gag is that the actors weren't made up to look any younger — they are just dressed in Disco-era fashion and with longer hair (including Nordberg [O.J. Simpson] with a Funny Afro so big he can't get through a door). Even more absurd, the Anna Nicole Smith character appears as a grown woman in the disco scene, even though the actress herself had barely reached puberty when the '70s ended.
In a flashback scene, two girl scouts end up in a bar room brawl. One of them smashes her head against a jukebox causing it to play The Bee Gees' "Stayin' Alive" whereupon everybody in the bar starts dancing. Arguably the earliest example in Western media, as Airplane! was filmed in 1979-1980, just as the anti-Disco backlash was beginning.
Parodied in a later scene where a DJ announces "This is WZAZ, where Disco lives forever!" shortly before the title airplane destroys the WZAZ radio tower.
In Mystery Men, Casanova Frankenstein employs the Disco Boys as henchmen, and there is a full Disco Room in his castle.
Disco is a Running Gag in You Don't Mess With The Zohan. This has more to do with Disco surviving outside the States for some time after it "officially died". Naturally, immigrant characters assume that it's still big in the US.
In an episode of RoboCop: The Series, Virtual Ghost Diana gets corrupted by a computer virus and turns a bit nuts. As a result, she transforms her Hacker Cave into a full Disco, complete with blaring music, stroboscopic lights and real laser fire! Once he makes the music stop, Murphy finally comments that he always hated Disco.
Whose Line Is It Anyway? had "Disco Boy" and "The Disco Kid" in the "Superhero" games. Greatest Hits and Song Styles did Disco from time to time.
A fairly extreme example, Pain Of Salvation is a fairly dark and brooding progressive metal band, with huge spiralling concept albums about the existence of God and a fair bit of deep introspection. Track five on their album Scarsick is called "Disco Queen". It's a bizarre 7/8 grooving Disco song. With falsetto vocals. Which go "You're my DISCO QUEEN! Let's Disco! Ooh-ooh oo-ee oo-ee, AHHHHH!" Although this is, of course, ming-mong Kryptonite, it's actually pretty good. They used it as an encore for the entire tour. It is extremely entertaining to watch the big, hairy, tattooed metalheads do the John Travolta-dance from Saturday Night Fever during said song.
Kylie Minogue owes her entire career to this. Her career had been fairly run of the mill until the disco-themed album Light Years was released and her fame skyrocketed, with no signs of ever slowing down for a long time to come.
In Earthworm Jim 3-D, there is a whole stage devoted to a Disco. Which mixes this trope with Everything's Deader with Zombies to form the stage "Boogie Nights of the Living Dead". The stage comes complete with a weapon called the "Funky Gun".
Skullmonkeys includes The 1970's as a collectible pickup scattered around levels. Whenever the player picks up enough of them, they're transported to, you guessed it, The 1970's. Accompanied by this music.
Jimmy T. from the WarioWare series is a Disco fiend, as is the rest of his family. They all wear multi-colored Funny Afroes, shades, and bell-bottom pants.
Dungeon Keeper 2 has casinos, and when a creature wins the jackpot, everyone around it starts dancing to "Disco Inferno" by The Tramps.
Dance Battler maestre Eddy Gordo in the Tekken series started off with an alternate "outfit" that was treated as a (relatively obscure) alternate character, Tiger Jackson. No word yet on whether Capoeira works with a disco beat in real life..
The "Dance Battle" in Bookworm Adventures Volume 2, which doubles as the Big Lipped Alligator Moment of the series.
In Paper Mario: Sticker Star, when Mario uncovers some Boos he must fight, the Boos suddenly start dancing to disco music while Mario joins along before the fight commences.
In Code Lyoko episode "Straight to the Heart", it is revealed that Jim is a former Disco dancer. Though he considers this an Old Shame at first, in "William Returns" he gains some fans and makes a return as "Paco, King of Disco".
In the Tiny Toon Adventures episode "Gang Busters", Hampton keeps messing up the music genre the characters are singing (rap), and one instance has him disco dancing while Fifi, Shirley, and Elmyra sing "Disco Inferno".