[TROPER enters, pursued by a BIG LIPPED ALLIGATOR].
[audience laughter and head-scratching]
In theater, a Big Lipped Alligator Moment may occur to allow for a costume/scene change, because the songwriters wanted to insert a "catchy" song (and plot be damned), or because it makes a part more attractive to "name" actors... which doesn't hurt the box office.
The catchy "One Night in Bangkok" in the musical Chess. Freddie/the American sings about going out partying in Bangkok at the beginning of the second act, but the song has no bearing on the plot of the musical as a whole, other than setting the scene. The song was (wisely) marketed to promote the musical, and actually reached a high point on the music charts. Ironically, more people are familiar with the song now than the play it comes from.
In some versions of the story, the song plays as Freddie goes out in Bangkok and gets beaten up. Which makes it a little more relevant.
"Brush Up Your Shakespeare", from Kiss Me Kate. The two gangsters have found out that the debt doesn't have to be paid, Kate's actress has decided that she loves her ex-husband after all, and the gangsters are leaving the theatre after a day's work... when the Fourth Wall comes crashing down, the pair are in front of a curtain, and they start tapdancing and singing about the virtues of Shakespeare as used in the seduction of women.
The Porter Scene in The Scottish Play is either a welcome bit of comic relief in the middle of a harrowing story, or else a completely incongruous digression possibly thrown in by some other writer who preferred fart jokes to serious theatre.
The scene also serves to cover the actor's costume change. Without the interlude Macbeth has two lines in which to wash off the blood from the murder.
There's another scene in Macbeth that is cut out of most film versions, where Hecate herself comes to the Weird Sisters and yells at them for giving Macbeth this information instead of her. This scene does not alter the plot as it does not result in the witches trying to correct their mistake or even doing anything about it. In fact, there's even a fairly common hypothesis that the scene was really a last-minute addition by someone else, or demanded by someone else, as it has nothing to do with the rest of the story.
The stage adaptation of Chitty Chitty Bang Bang features one toward the end where the King, Queen, and everyone else in the palace of Vulgaria break into a dance called "The Brazillian Samba" which was not featured in the film (or the book it was very loosely based on). Still, it was the King's birthday, but aside from that it has nothing to do with the plot.
The play My Name Is Rachel Corrie is about a young woman by that name who was killed by an Israeli bulldozer demolishing a Palestinian family's house which she was attempting to protect. The play opens with her apparently reading a journal entry which describes a bizarre, seemingly schizophrenic hallucination. Then the play goes on as a monologue narrating her life and thoughts leading up to her death. At no point is the opening scene explained or referred to again, and she never shows any other signs of mental illness or hallucination.
In the musical The Pajama Game, the opening of Act 2 called "Steam Heat", a quirky song and dance routine introduced into the show as a union morale-booster. The song was a pop hit in the 1950s, and the dance did a lot to advance the career of Bob Fosse, but it's still weird.
Adler and Ross, the songwriting team of Pajama Game, included a completely pointless song in their other show (Damn Yankees) as well, "Who's Got the Pain?"
The Cole Porter musical Something For The Boys, now obscure though a hit in 1943, had a number called "By the Mississinewah," in which the show's two leading ladies dressed as squaws, the costumes being Braids, Beads and Buckskins at their campiest, singing about living a bigamous life in Indiana. The song is ludicrously corny, totally unlike the smart songwriting Cole Porter is best remembered for, and the lyrics go into Gratuitous French for no reason.
The second scene of the third act of George Bernard Shaw's Man And Superman, Don Juan in Hell, is a dream sequence where Don Juan and the devil argue about life and the afterlife. It's usually removed from productions of Man and Superman because it's fundamentally a very long Big Lipped Alligator Moment, but it can be performed as a stand-alone one-act play without confusing the audience more than the material itself already might.
In Bye Bye Birdie, the song Put on a Happy Face features the male protagonist stopping the plot entirely in order to cheer up a random girl before getting into an extended dance sequence. The song added nothing to the plot and was only added last-minute to help put some spark into the show. It worked, and it's now considered by many to be the best song in the show.
The 1963 movie version managed to hook this sequence into the plot by having the female character be depressed about something in the story.
The new Billy Elliot musical has one, a biggie. There's this quite serious and slightly depressing moment, then a break and then... There's suddenly something, something christmas and Margaret Thatcher and... that whole ordeal lasts about 10 minutes before the musical returns to 'normal'. In the meantime, you'll just sit there and wonder what the hell just happened... And that state will hold on for a good bit after the moment.
Billy Elliot pretty much counts as a straight up Bizarro Musical, there are so many BLAM moments scattered throughout. Especially Michael's number about... *ahem* "self expression".
In Gilbert and Sullivan's Utopia Limited, the second act opens on Zara and Captain Fitzbattleaxe, the young couple in love, and Fitzbattleaxe... sings a song about how he's much too much in love to sing romantic ballads effectively, as his voice keeps breaking in the high notes, complete with intentional flubbing of the high notes. In an opera. Fourth Wall? What Fourth Wall?
In The Pirates of Penzance, everyone drops what they're doing for a moment to sing a song about the beauty of poetry.
King Herod's Song in most versions of Jesus Christ Superstar. He shows up for one scene with a court of over-the-top decadence to sing a jazz number at a dumbstruck Jesus, without so much as a snippet reprised elsewhere in the show, with the closest thing to a mention after being Pilate asking, "was Herod unimpressed?"
The title song is arguably one itself. It comes in out of abso-flipping-lutely nowhere toward the very end of the show, and it's sung by a character who's supposed to be dead at that point...
It makes sense plot-wise based on Herod's role in the source material sometime, but the song is still jarringly lighthearted compared to the tone of the show. Since angsty musicals not something that Broadway audiences were accustomed to in 1971, Herod's number was most likely thrown in just so the audience would have something they could relate to.
The lightheartedness comes from the fact that it's melodically based on a failed pop song Lloyd Webber wrote a few years previously called "Try It and See", which was a cheerful song about a Manic Pixie Dream Girl convincing the object of her affections to give their relationship a shot. This makes its reuse as Herod's song make even less sense.
There's a part of the "NYC" number in the musical Annie where a young woman (listed in the script as "Star To Be") sings about how she just arrived from out of town and plans to make it on Broadway. She leaves before the number is over and is never seen or mentioned again. The 1999 TV movie adaptation handled this bit by presenting it as part of a fluffy Broadway show Annie and Warbucks go to see during their whirlwind tour of the city, with the Star To Be (played by Andrea McArdle, the original Broadway Annie) the show's leading lady.
The drinking quintet in the second act of Marschner's Der Vampyr seems to mainly be an excuse to have a drinking scene; it interrupts the plot with characters who had one or two lines previously and whom we never see again, and ends abruptly with the discovery of Emmy's death.
Subverted in An Italian Girl in Algeria by Rossini, with the scene where Mustafa is given the honour of being a Pappitache (silent eater) in a ceremony where he swears to eat, sleep, drink and not complain. What makes this a subversion? It does lead to the final resolution.
The Renaissance Festival comedic swordfighting group Fight School has a bonus fight sequence on their DVD of Fight School II: Reloaded, where two of the Fight Schoolers, Hamish Stuart and Captain Romero, fight each other with daggers while the other two (Nymblewicke and Dash Rippington) follow them around observing. The fight (which was specially filmed for the DVD) takes them all over the grounds of the Maryland Renaissance Festival, and in the middle of it, they stop to rest at the Dragon Inn. There, they are suddenly confronted with a zombie bartender, and a trio of zombies. Hamish and Romero team up to face the zombies (Nymblewyke instructs them to do in the zombies by snapping their necks), and soon overcome these unexpected opponents. Afterwards, Hamish and Romero resume their dagger fight, leaving the Dragon Inn followed once again by Nymblewicke and Dash, and more or less go on as if the strange zombie incident never happened.
Spider-Man: Turn Off the Dark is basically made of this trope. But the shining example? In the second act Arachne (the figure from Greek Myth) sings a song about how awesome shoes are with her Spider-Furies. This includes what is basically an 8 legged Burlesque act complete with what seems to be on-stage masturbation.
It has since been removed from the show.
Contact in Rent, where the cast basically has a staged orgy under a sheet during a dream sequence.
PLAYZONE 2009 starts as a perfectly fine self aware musical. Then someones phone rings. Cut to a minute later wherein half the cast is yodeling around the stage dressed as cowboys singing about Cellphone Heaven. And mechanical horses.
Sweet Charity has the Irrelevant Act Opener "Rhythm of Life" when Oscar and Charity go to church for their first date. The movie attempts to give it some relevance by showing Oscar get over some of his neuroses while hiding from the cops after the number is over, but the play has no such scene; Charity and Oscar simply appear after the number is over, say, 'Where did you find those people?', and leave. It's still awesome.
The Addams Family musical had a ballet in which Uncle Fester dances with the moon. It's never mentioned before that, and since the rest of the musical is staged pretty realistically, the Disney Acid Sequence that is Fester dancing with the moon seems thrown in just to show off.
Hair's second act starts out with a literal acid trip, where Claude sees such figures as Ulysses S. Grant and Scarlett O'Hara, nuns kill Buddhist monks, Buddhist monks set themselves on fire, Abraham Lincoln sings a song, but is played by a black woman...and other weird things. Claude wakes up from his acid trip, says 'where did you GET that shit?' and we move on with the plot, such as it is.
The revival of Into the Woods had one when during 'Hello Little Girl' a song sung by the Big Bad Wolf to Little Red Riding hood, another wolf appeared and began chasing the Three Little Pigs. The pigs disappear and are never referred to again. It seemed to have been done because Cinderella's prince plays a wolf (to emphasize his predatory nature) and the director wanted both princes to play wolves. It was still odd.
In the original London production of Les MisÚrables, the song 'Little People' came pretty much out of nowhere, stopped the plot and had no further bearing on what went on. It has since been edited and put in a place where it makes more sense, and is no longer a Big Lipped Alligator Moment. But it WAS.
Light In The Piazza had one when during an emotional scene sung entirely in Italian, Fabrizio's mother, a character who does not speak English, turns to the audience and begins explaining what's going on. This device is never used again.
In Avenue Q, Brian's song "I'm Not Wearing Underwear Today". He's not opening a comedian. It's not an open-mic-night. He's opening for Lucy The Slut, who sings a very different kind of song. Naturally, his fiancee is displeased.
In Hemet - a small town in Riverside County, California - there is an annual dramatization of Helen Hunt Jackson's Old Western melodrama Ramona held outdoors, with the front of a house serving as a Spanish rancho and the existing hills and wilderness around the amphitheater filling in for the Indian backcountry. The play is about as corny as you'd expect a work based on a 19th-century popular novel to be, with some embarrassing Mood Whiplash (lines recited in "wacky" frontier dialect being followed soon afterward by one of the main characters showing up and screaming "THEY SHOT MY FATHER!") - but the most jarring sequence has to be when the plot of the play stops entirely so that a traditional Indian dance can be presented, and then this dance goes on for several minutes. (The plot was actually pretty simple and not at all hard to follow, but it was still odd to see it interrupted.)
In Aida, Princess Amneris sings a song about how style and fashion is the only thing that she's good at in life. Then, there's about a three minute-long fashion show of just models walking down a "runway" in extravagant dresses. Complete with flashing lights.
Possibly subverted, in that the song is later reprised, where she sheepishly admits that she only hides behind her shallowness out of fear that fashion is all she will ever be good at, and asks Aida to help her become a better ruler in training.
The musical comedy Drood has several, by the nature of the play. Most notably is 'Off To The Races' where all the minor characters come in, sing the 'stage house's theme song' and then leave, for essentially no good reason. Also notable is 'Never The Luck' where a secondary character is allowed to have a song because 'the first act is almost over' and the Chairman is feeling generous. It adds nothing to the plot, other than establishing Bazzard's desire to be a lead actor (which had already been established in 'No Good Can Come From Bad') and is never brought up again, except for a few lines in his version of the Confession (it's a weird play.)
"Who Will Buy," from Oliver!. Even more so in the movie, which is 13 minutes long, and has almost no singing.
In the actual theatre production has these
I Shall Scream
Oom Pah-Pah: The producers even admitted it was a BLAM. The Movie gives it a purpose with Nancy trying to cause a distraction so she can smuggle Oliver to Mr Brownlow.
and the aforementioned "Who Will Buy"
The musical Memphis features a BLAM involving an almost-literal alligator. During a broadcast of the protagonist's live TV show, a major supporting character named Gator suddenly appears wearing an alligator costume to perform his "famous Gator Dance". No mention of his talent for "gator dancing" is made before or after this scene, and the bizarrely comical number is so out-of-nowhere and distracting that, despite the obvious intent to use it as bland background business for an important downstage conversation, this troper had trouble focusing on anything but the Gator Dance.
In the Spanish musical Hoy No Me Puedo Levantar, the song about Salvador Dali/Laika in the middle of a Mushroom Samba is this.
In the 1938 Rodgers and Hart musical I Married An Angel, midway through the second act, at a point where the spirits of the protagonist and audience desperately needed raising, a song and George Balanchine ballet in praise of the Roxy Music Hall was inserted. This gratuitous spectacle, which included surrealism for surrealism's sake, blatantly had nothing to do with anything that came before or after it.