Parents Walk in At the Worst Time

An older teenager, or young adolescent goes to his or her room with a friend of the opposite gender. At some point, his parent will find some reason to barge in.

This plays out in two ways:
 * Type 1: Boy and girl are making out, or about to. Parent will bring contraceptives if this was expected, or a very shocked look if it wasn't. (Warnings and snacks could be brought in either circumstance). If unexpected, Hilarity Ensues, though we usually don't see it. Awkwardness between parent and child will also ensue.
 * Type 2: Boy and Girl are doing something innocent, like studying or playing board games, and the parent walked in expecting that they were making out.

Related to Moment Killer. A subtrope of Interrupted Intimacy. For children walking in on their parents, see Primal Scene.

Comics
"Peter: ...We appreciate the thought -- but we were already warming our bones. MJ: Next time, could you knock? Aunt May: Knock? Oh dear! Oh my! I'm so sorry! I keep forgetting you two are married... [from behind the just-closed door] Oh dear!"
 * Web of Spider-Man #50: After Peter and Mary Jane (still newlyweds at this point) settle in for the night (and some quality time), Aunt May barges in on them with a tray of hot cocoa to "warm their bones."

Film

 * In Mean Girls, while Regina is getting hot and heavy with her new boyfriend, her mother (or rather stepmother, played by Amy Poehler as a nymphomaniac bimbo trophy wife) comes in asking them if they want anything, whether it's snacks or condoms.

Literature

 * In the Doctor Who Eighth Doctor Adventures, Fitz's mum mentions that when she had out of body experiences in her sleep and looked through his window she saw him doing something which she considered too embarrassing to specify. So it could be this or another trope. Sometimes, even if you lock the door and wait for everyone else to go to sleep, you still just can't win...

Live-Action TV

 * In one episode of Home Improvement, Jill walks in on her son Brad and his girlfriend making out in his bedroom. This gets Brad in trouble because Brad wasn't allowed to have girls in his room.

Web Comics

 * In Sabrina Online, when Amy and Thomas have sex on her bed, her mother is outside asking if they need anything. Amy's father tells the mother to leave them alone.
 * In Questionable Content, Faye's sister Mandy came out as lesbian to her mother because of this trope.
 * In Red String, Hanae's mother finds out her daughter is a lesbian this way. She doesn't take it well.

Advertising

 * On an advert for insurance (perhaps Norwich Union?). A teenager's grandmother approaches his room with a cup of tea and is greeted by cries of 'Yes! I love you!' from the room. Of course, he's actually just been informed how cheap his insurance quote is.

Anime and Manga

 * Rosario + Vampire has a variation. When Tsukune goes back home for a few days, the harem follows him. Moka shows up as the girlfriend. However, the rest of the harem managed to get into his room without his mother noticing. When his mother shows up bringing tea for the two, she ends up seeing a Lover Tug of War.
 * Narue no Sekai has a different variation. When Narue visits Kazuto (and visits his room, as is standard in a Japanese household), Kazuto's mother and older sister walk in repeatedly because they have trouble coming to grips with the idea Kazuto has a girlfriend.

Comics

 * One strip of Zits had Jeremy and his girlfriend studying in the kitchen, so of course Jeremy's parents come in every five minutes, getting "good, clear water!", taking out laundry, changing light bulbs, dusting the top of the fridge...
 * Robin (Tim Drake) from the Batman series had one particularly amusing experience. His girlfriend Arianna tried to seduce him in lingerie but he turned down the opportunity, saying that they weren't ready for it. They ended up talking all night but when her relatives walked in on them (with Arianna still in her lingerie), they got the wrong idea and chased out Tim in rage.

Live-Action TV

 * Played with in Dharma and Greg: Dharma's ultra-hippy mother would bring a teenage Dharma and her various boyfriends post-coitus snacks and drinks.
 * While Greg (Dharma's husband) was uncomfortable, she was delighted.
 * Implied in Buffy the Vampire Slayer. When Anya goes to Xander's house, we see the two of them quickly heading to the basement, Xander saying, "Thanks for the snacks, Mom!" Anya remarks that she enjoyed said snacks.

Film

 * Transformers, Sam Witwicky tries to find a small chip placed on his treasure glasses belonged to his grandfather, which he forgets where he left them in his room, and get Mikaela to help him. It gets too noisy that Sam's parents go up to check him out. His mother gets completely wrong ideas both before and after she finds the girl in his room.

Unspecified - Were They or Weren't They?
Please specify and move accordingly

Advertising

 * There is a series of commercials for Pocky that involve this trope.

Anime and Manga

 * In the first Higurashi no Naku Koro ni arc Keiichi's dad comes to bring Rena and Keiichi tea and snacks. In the manga it would have been a moment killer if Rena hadn't left and if she had talked to Keiichi. The fact Keiichi was talking on the phone about something secretive and he was suspicious of Rena makes him even more paranoid..

Live-Action TV

 * In a season two episode of Glee, before Kurt and Blaine get together, Blaine is too drunk to drive after a party, so they bring him back to Kurt and Finn's house. In the morning, Kurt's dad walks in to find Blaine in Kurt's bed and is quite shocked, even though they are both fully dressed.