Interrupted Intimacy

Good thing they didn't show up later, that could've been traumatic.

A couple is about to have sex, or are in the midst of the act, but another person interrupts somehow. They have to stop to deal with the interruption. This trope can be played for comedy, drama or both. Can often lead to a Relationship Reveal. If they choose to keep going, it is Coitus Uninterruptus. If they try and keep things secret (if there is a knock on the door), it could lead to a Closet Shuffle. A subtrope of Moment Killer.

Compare to Caught with Your Pants Down for the solo version of the trope. A supertrope of Primal Scene and Parents Walk in At the Worst Time. Sister Trope to Sorry to Interrupt.

No real life examples, please; this is All The Tropes, not Tropes After Dark. Also, we'd be here all day.

Examples of Interrupted Intimacy include:

Anime and Manga

This happens to Lupin and Fujiko, in The Secret of Twilight Gemini. Just as they're getting started, Sadachiyo and his men bursts into their hotel room to assassinate Lupin, forcing him to bail in his underwear; which leaves Fujiko stark naked with nothing but a bedsheet to defend herself!
- Averted the second time 'round, which takes place in a Morrocan police station! Lupin scores.
Happens near the beginning of Vitamin. The protagonists boyfriend forces himself onto her while they're in school, and a classmate sees them.
Ranma ½: It comes off like this when Akane finds Ryoga on top of a female Ranma in bed, right after Ryoga forced open Ranma's shirt. Ranma himself assumed this was the case. Because while Ryoga was only checking to see if Ranma had a weird mark, our lovesick hero was merely waiting for the love-making to begin.
Yuugen Kaisha has a scene like this, in incident file 03. Detective Karino drops by Nagasuki's office to question him, not knowing things were heating up between Nagasuki and his secretary! So when he opens the door, he gets an eyefull, though the audience doesn't get to see anything.

Fan Works

Played for Laughs in the appropriately titled, This Closet's Lock is Broken, when Soifon accidentally bursts in on Yoruichi while she's having sex... with a mod soul designed to look and act like her! (Both are girls.)
In a canon chapter of Harry Potter and the Deathly Hallows, Ginny lures Harry into her bedroom (with the door closed) to give him a birthday present to "remember her by", and they begin to kiss very passionately, but are interrupted by Ron barging into the room. There are many stories that speculate that, had Ron not interrupted, Harry and Ginny would have had sex.
Lucky Star: This trope probably scars Kagami for life in Stars Above when she accidentally walks in on Tsukasa and Miyuki.
My Immortal. When Draco and Ebony have sex in the Forbidden Forest, Dumbledore barges in out of nowhere, yelling "WHAT THE HELL ARE YOU DOING YOU MOTHERFUKERS!"

Film

Running Joke in Shakespeare in Love.
In Cemetery Man, Francesco Dellamorte and his mystery woman make it on top of her husband's grave, at her request ("He would have liked to know.") Unfortunately, in this particular cemetery the dead are prone to rise seven days after burial - her husband digs his way out, catches them mid-act and promptly takes a bite out of his wife's arm, whereupon Francesco impales him with a cross.
In Hot Tub Time Machine Adam, Nick and Jacob walk in on Lou having sex with Adam's sister, meaning Jacob witnesses his own conception... sort of. When he tries to attack Lou, he disappears, and Coitus Uninterruptus has to ensue to ensure Jacob lives.
Running Joke in in Going the Distance too—from Dan DJ'ing Erin and Garrett's first hook-up, to her sister walking in on them having sex on her dinner table... and her husband eating a midnight snack to them walking in on her sister and her husband dry-humping.
In the Japanese movie The Eel, the protagonist finds his wife having intercourse with another man and kills him right then. He spends eight years in prison; his life right after release is the actual story.
Happens in the British film Sir Henry At Rawlinson End when in a flashback Seth Onetooth finds his wife Rosie carrying on with Henry's brother Humbert in the bushes. This leads to Humbert "accidentally" getting shot by Henry, and explains why his ghost cannot rest until it has found trousers.
In The Secret of My Success, Brantley (Michael J. Fox) ends up having an affair with his boss's wife, Vera ({{{1}}}). When she comes to his office looking for seconds, they get busted when her husband shows up unexpectedly to talk to him.
In Schindler's List, Schindler is having sex with his mistress, when he's informed that his accountant, Stern, has been mistakenly put on the train that takes Jews to the death camps. Schindler manages to save him just in time.
In Make the Yuletide Gay, Gunn and Nathan are in Gunn's room stripping down to have some fun time, when Gunn's mom comes in to make sure the boys have enough sheets for their beds.
Friends With Benefits has Jamie's mom walking in on Dylan and Jamie in the middle of the act.
In D.E.B.S., Amy and Lucy's relationship is exposed when the other members of D.E.B.S. burst in on them in bed together.

Literature

Captain Armand Pahner walks in on two of his sergeants (Eva and Julian) in the Prince Roger series.
- Additionally Julian deliberately arranges for this to happen to Roger and Despreaux on multiple occasions. By monitoring the biometrics in her combat suit (specifically pulse and blood pressure) he can tell when they are arguing and when they... aren't.
A large portion of the drama in A Song of Ice and Fire is sparked by Bran seeing Cersei and Jamie Lannister having sex.
Locke and Sabetha are just starting to get it on in The Republic of Thieves when the Jerkass mage Patience, who had been watching all along, pops into visibility to order Locke to stop Dating Catwoman like that.

Live-Action TV

Abby has to hide under Brody's bed when her drunk brother Richie turns up for a midnight visit in Against the Wall.
Lip Service, in the fourth episode when the interruptor turns out to be the husband of one of the women who is hoping to watch the two of them have sex.
Running gag in Six Feet Under. Nate and Brenda get interrupted twice, first by Brenda's brother, then Nate's mom.
Game of Thrones:
- The last scene of episode one. With horrific and long-reaching consequences.
- Played for Laughs when Jamie Lannister walks in on his brother at brothel in Winterfell and tells him to hurry up, then proceeds to send in more prostitutes in order to hurry him up.
Played for Laughs in a The Big Bang Theory episode. Leonard was sleeping with a girl named Joyce Kim and was having sex with her when Sheldon decided to interrupt by knocking on the door. Leonard was thinking of ignoring him, but Sheldon knew he was being ignored. Sheldon then came in to remind Leonard of their Roommate Agreement. Due to its terms, Joyce decided to leave.
- This was actually a good thing for Leonard. She was a North Korean agent trying to get information about a project he was working for. He even admits Sheldon probably saved him from going to federal prison. Again, Played for Laughs, but still.
Friends has Monica forced to hide under the sheets and Chandler pretending to have A Date with Rosie Palms when Joey walks in on the two of them in London.
An episode of Veronica Mars has an (adult) hacker's relationship with a student (minor) at the school being exposed by Veronica and her camera. She even says "It's satisfying to be the interruptus in somebody else's coitus."
Combat Hospital has Graham interrupting Simon and Rebecca at the undressing-and-foreplay stage with some pretty serious news for Simon. Rebecca hides, then slips out the back.
Boy Meets World had a comically extreme example: Cory and Topanga are about to consumate their marriage when the police burst to the hotel suite in and arrest them (because they inadvertently stole someone else's wedding thanks to Eric).
Chuck has Chuck and Sarah on the run in order to find Chuck's father, and finally look like they will resolve all that sexual tension after sharing a bed at a motel, only to have Casey track them down and arrest them as they are in the midst of some serious heavy petting.
Rookie Blue has Sam and Andy being interrupted by Sam's boss. Since he is undercover and working for a very nasty drug dealer, this is quite serious and is Played for Drama.
Two Broke Girls: How Max finds out her boyfriend is cheating on her in the pilot.
South of Nowhere: How Spencer's family learned that Spencer was gay.
In Torchwood, Gwen walks in on Jack and Ianto right in the middle of a make-out session in the office.
In the Babylon 5 Grand Finale, Emperor Vir Cotto is interrupted while in bed with two women. This is initially played for laughs, but quickly shifts to drama as he realizes that the visiting Ranger is delivering the news that Sheridan is about to die.
Modern Family's "Caught in the Act" episode during the second season. All three Dunphy children walk in on their parents.

Music

Happens in the Warrant song "Cherry Pie":

Swingin' so hard
We forgot to lock the door!
In walks her daddy
Standin' six foot four!
He said "you ain't gonna swing
With my daughter no more"!

Tone Loc's Wild Thing has the same thing happen (in this case the girl's mother interrupts them), but with more benign results:

I didn't know what to say; I was hanging by a string
She said "Hey, you two, I was once like you and I like(d?) to do the Wild Thing."

Web Comics

In Ménage à 3, this is a Running Gag. Nearly every time Matt has sex, no matter with whom, someone walks in and interrupts him.
In Misfile Ash and Emily end up walking in on Kate and Harry having sex. Oddly enough Kate is only mildly embarrassed and glad that it was at least someone she knew. Ash on the other hand looks like she could use a jug of Brain Bleach.

Western Animation

On Archer Lana dumps Cyril after walking in on him having sex with Framboise from ODIN.