"You know how in some RPGs you start off in your lovely idyllic green grass village where smiling neighbors bid you how-do-you-do that is virtually guaranteed to get Hiroshimafied before the second act?"
So you've moved up the ladder in life. You have a loving foster father, and an adorable foster little sister. You steadily rise in your occupation, what's with being a phenomenally talented person. Your fiancee is the son of one of your higher-ups. The aforementioned little sister is going your path, and is an even more talented person than you. Things will be getting even better in the future, right? The answer is, unfortunately, a profoundly resounding NO, because your name is Yomi Isayama.
In Puella Magi Madoka Magica, Mami Tomoe is killed almost immediately after she finally finds contentment in her life — directly on the heels of a monologue about how wonderful she feels, in fact. It's implied that being happy indirectly caused her death — it made her reckless.
Happens in the first episode of D.Gray-Man, a couple is literally split up in their day of their wedding, just when the women was thanking God for their happiness (and perharps Killed Mid-Sentence). It's pretty much someone giving them the finger, and the now turned Anti-Hero blames God.
D.Gray-Man is absolutely in love with this trope. You can pretty much expect that any character who is both a) happy with his life and b) not a main character is going to either die or have someone he loves die.
In Neon Genesis Evangelion, it appears that the universe goes out of its way to horribly destroy anyone that even tries to be happier. For example, we have Kaworu Nagisa, the only person in the entirety of the series which is shown to love Shinji unconditionally. He doesn't even last the episode he appears in.
Also in End of Evangelion. When Lilith begins the Instrumentality of mankind, various Rei dopplegangers take the appearance of people that each human loves (such as Misato for Makoto Hyuuga, Yui for Fuyutsuki, and Ritsuko for Maya), giving them such pleasure and happiness before destroying their AT field and reducing them to a puddle of orange goo.
In Saikano, you know that whenever a secondary character is having a happy moment, joking and/or laughing as a break of the horrors of war, they are about to be killed in a short moment by an enemy bombing or attack.
Medaka Box: Time will tell if it sticks but as of chapter 154, Zenkichi has been killed right after having his marriage proposal accepted by Medaka.
Higurashi no Naku Koro ni: At the beginning of every arc (from his perspective), Keiichi notes that he much prefers his new life in Hinamizawa, and is surrounded by people who all know and love him. Then someone mentions the Watanagashi festival or the murders, and it all goes downhillfromthere...
Also, Rika in Dice-killing Arc. She's just defeated the "Groundhog Day" Loop that she's been trapped in for centuries, has two months of happiness... then gets hit by a truck.
In The Ultimates, Quicksilver and the Scarlet Witch are a couple, but how happy they are about it is the portent of tragedy.
Though nobody dies, this is just one of many reasons why Spider-Man fans hate One More Day. Peter and Mary Jane have been Happily Married for about twenty years (real-time). But we can't have that; how are we going to get Peter caught up in Love Triangles? (And this isn't the first time; they previously tried to kill MJ off in order to make Peter a swinging single again.)
Subverted in Punisher Max. Frank wasn't happy with his life since he discovered his inner Blood Knight in 'Nam and was dissatisfied with peace. Frank is haunted by the fact that he had asked his wife for a divorce right before she and their children were killed in the botched Mafia hit.
The Incredible Hulk is not the Hulk unless he's upset. Therefore it's kind of a Foregone Conclusion that any happy relationship he is currently in will end poorly at some point in the near future.
The recent Death of Spider-Man arc's prelude in Ultimate Spider-Man was this for Genre Savvy readers - even without the title, the fact that everything in Peter Parker's life was going absurdly well was a big clue that there was much badness on the way...
The Mothman Prophecies. John and Mary are ecstatic over their purchase of a new home, laughing on the car on the way back to it. And then disaster strikes...
What Dreams May Come. The first ten minutes have Chris meeting his future wife, having kids, and laughing. And laughing. And laughing. And then his kids are killed offscreen, then he dies, then his wife commits suicide...
Parodied in Hot Shots! has this one guy happily talking to his wife just before he went to fly. He never came back.
Oh, it's better than that: he's not only happily married to a perfect gal, but also has yet to sign his life insurance policies and he just recently discovered the secret to world peace and who really killed JFK. But he'll deal with all that stuff after this one last mission. His callsign, by the way, is "Dead Meat."
Parodied in Walk Hard, where the main character's brother's every line involves mentioning how happy he is to be alive. He is immediately sliced in half in a machete battle.
In The Great Escape, Big X comments to one of his colleagues that he's never been happier than when he was at the Stallag working on escape plans. Less than a minute later, he and all of the other recaptured prisoners present are murdered by the Gestapo.
The Fellowship of the Ring: You live in an idyllic little town where everything is green lawns, simple folks, and blue skies. You spend your days in the woods, the hills, little rivers... When all of a sudden, your uncle disappears, his best friend tells you you have to leave your home immediately, and big scary horsemen with big scary swords stab you with a soul-stealing dagger, leaving a wound which will never heal.
Leslie from Bridge to Terabithia. She was, in fact, inspired by a real person the author of the original book knew.
Lord Foul's Bane. Thomas Covenant lampshades this, pondering if he had lived an entire lifetime's worth of laughter before the discovery of his leprosy.
Ernest Hemingway has the main couple of A Farewell to Arms quite happy, having escaped the Italian manhunt to Switzerland. While there's a level of self-destruction going on - they're living entirely on credit - the characters don't seem particularly bothered. Cue Death by Childbirth.
This happens a lot in Warhammer 40,000 fiction. If you ever see ANY peaceful farmers or other common people, living pleasant lives and thanking the God-Emperor daily for the blessings He has seen fit to bestow upon them, you can expect a war which will kill most or all of them to break out within the chapter.
It hasn't happened yet, but in Thud!, it's revealed that the greatest fear of Sam Vimes, who over the course of the Discworld series has gone from a drunken wreck of a night watchman to a public VIP and happily-married father, is that this is going to happen someday, if not to him then to his infant son.
Roger Ebert referenced this trope in his book The Little Book Of Hollywood Cliches. In his list of the "top movie characters likely to die," he says:
''The person who says "I've never been happier than I am now" is not going to live to see the end credits.
Finnick Odair, a short time after his wedding to Annie Cresta in Suzanne Collins' ''Mockingjay’’.
Sisterhood Series by Fern Michaels: The very first book, Weekend Warriors, starts off with Myra Rutledge and her daughters Nikki Quinn and Barbara Rutledge, all three of them happy as they can be. Then Barbara gets struck and killed (along with her unborn child) by a drunk hit-and-run driver exploiting Diplomatic Impunity. Cue the Heroic BSOD and the formation of the Vigilantes!
Danielle Steel often starts her book with an ad nauseam description of how perfect the protagonist's life is. Which is often a good sign that it's all going to fall apart very soon.
In a late episode of The Commish one of the officers was promoted to detective. Cue Car Bomb.
Marian from Robin Hood joyfully, fiercely, blissfully shouts: "I love Robin Hood! I'm going to marry Robin Hood!” (This after years of not being able to admit her love for mostly political reasons.) A second later, the hypotenuse of their love triangle runs her through with his sword and she dies.
Scotty: "I cannot go on! I'm tired of happiness. I'm tired of comfort and pleasure. I'm ready! Kill me! Kill me!"
[Kirk and others mime shooting hand phasers, complete with vocalized sound-effects]
"Goodbye, cruel universe."
McCoy: "He's dead."
Android: "You...cannot have killed him. You have no weapons."
Kirk: "Scotty! Scotty's dead. He had too much happiness. Now he's happier; he's dead. We'll miss him. Let us hear it for our poor, dead friend."
[human characters all laugh]
Everything Joss Whedon has ever written. If fans see someone happy, they know bad things are right around the corner.
One of the cruelest examples happens in Dollhouse, right after Bennett and Topher kiss. They're both happy, he's bouncing around like a schoolgirl, she's actually smiling for once in the episode, and then Saunders shoots Bennett right as Topher walks back in the room.
Joel Mynor has this as part of Death by Origin Story. After years of being supported by his wife he finally managed to make something that was a hit, giving him a huge paycheck. He decided to surprise his wife with it by secretly buying her a house and calling her to meet him at the address. She died in a car crash on the way. I mean... jeez.
Angel milks this for all it's worth with Cordelia and Angel at the end of Season 3. They've just independently realized they love each other! They're running (separately) to a romantic location where they can tell each other how they feel! So, naturally, one's going to ascend to the heavens, never to be seen again (sort of), and the other's going to be put in a box and sunk to the bottom of the ocean. And no, they never do express their love to each other.
Buffy and Angel. Relatively speaking, Buffy / Riley and Willow / Oz got off pretty easy.
Whedon embraces this trope. "Happy people make boring television."
LOST does this to Jin and Sun. After being apart for nearly two seasons, Sun thinking Jin is dead, Sun returning to the island only for Jin to be stuck in the '70s, Jin coming back to the present only to be moved to another part of the island any time Sun might find the group he's with and they finally reunite only for both of them to die along with Sayid in the next episode.
Joan of Arcadia featured the spunky new friend added into the second season who was quirky and happy and full of life and is then stabbed to death in an alley way for drama.
Ianto in Torchwood. Okay, happy might not be the exact word, but he's just managed to accept his relationship with Jack, tell his sister about it, and generally not be a blob of angst in a sharp suit... And then boom, incurable alien virus.
On Sisters, second-oldest sister Teddy was finally happy after years of trauma and preparing to buy a house with her new husband (who himself had been through years of hell), when he was killed via a Car Bomb by a crime lord he was preparing to testify against.
The pilot episode of the 2000 remake of The Fugitive spends the first 15 minutes establishing that Richard Kimble basically had it all—a beautiful wife he adored, plans to buy a house, discussion of starting a family—before it was blown apart by his wife's murder and his subsequent wrongful conviction.
After the crews split up in the third season of Farscape, the Crichton who went with Aeryn aboard Talyn got Harvey removed from his head, unlocked the wormhole knowledge in his brain and could now utilize it to get home, and hooked up with his Love Interest, basically accomplishing all of Crichton's goals on the show. We can't have that now, can we?
Used utterly without shame at the end of the Downton Abbey 2012 Christmas special. After Mary gives birth to her and Matthew's son, we get a few minutes of them sitting together in hospital, gushing about how happy they are and how Matthew falls more in love with her every day. Back home, the rest of the cast are discussing how far away the less certain times in their lives seem now. Then Matthew dies in a car accident in the last two minutes.
Game of Thrones: Robb Stark has things going exceptionally well for him at one point. He's been quite successful in his war, he just secured an alliance that would allow him a possible decisive victory, he's married and his wife is expecting. Then comes the Red Wedding. The TV adaptation played up how idyllic his life was compared to the novels.
Heavy Rain. At the start of the game, Ethan Mars has a blissful suburban life with his wife Grace and their two sons, Jason and Shaun. Then Jason is killed in a car accident and Ethan is put in a coma for six months. There's a Time Skip to two years later when Ethan is depressed, traumatized over the accident, separated from his wife, and has a strained relationship with Shaun who barely even speaks to him.
Max Payne: Life was good. The sun setting on a sweet summer's day. The smell of freshly mowed lawns, the sounds of children playing. A house across the river on the Jersey side. A beautiful wife and a baby girl. The American Dream come true ... But dreams have a nasty habit of going bad when you're not looking.
In Mass Effect 2, Jack will invoke this about herself if she romanced a male Shepard and dies as the second squad team leader.
Jack: Too many of them... I knew I'd get hit on this job. I was too happy... too happy with you.
Mother3 opens with Hinawa, Claus, and Lucas visiting their grandfather, happily playing with friendly dinosaurs, eating lunch, and preparing to depart for Tazmily in the afternoon. It's all downhillfrom there.