This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Ray Bradbury
The short story "There Will Come Soft Rains" describes the activities of an automated house, long since abandoned but still running on its programming. As the story progresses, it becomes clear that humanity was destroyed in a nuclear war at some point in the past (there is a reference to children's shadows burned into a wall). The house still runs, until it finally succumbs to decay at the end, but nobody will ever live there again. The title refers to a poem about how life will continue even after the end of humanity; the story basically says, "Not if we screw things up first". Haunting. (Incidentally the story can be read online here.
The most disturbing part of the whole story: The only living thing you see during the whole story is the family's dog, returning home to die from radiation sickness and starvation. Every man, woman and child should be forced to read this story. Do that, and it's a safe bet that the only place we will be launching any nukes will be straight into the sun.
What about seeing the silhouettes burnt into the wall of the house, showing just where the people were when the bomb went off? In particular, you get this set of silhouettes, showing a boy, a girl, both of them adorable, and the ball that they had been tossing between them.
Apparently this actually happened IRL in Hiroshima and Nagasaki.
The Russian animated adaptation of the story makes it worse. The house, instead of seeming maternal and friendly, looks and sounds like it would kill you at any given second. The family's fate is more gruesome. Instead of having their silhouettes burned into the side of the house, they were burned to ash while sleeping in their beds. The robot unknowingly dumps the family's ashes on the floor when it tries to wake them up.
Not to mention the voice of the house... dear God, the voice...
Tellingly, that adaptation also leaves out the following lines from the poem:
Not one would know of the war, not one
Would care at last when it was done.
Lots of Ray Bradbury stories fall into this category, esp if they've been made into Twilight Zone episodes, for example, "The Elevator", "The Burning Man"... For example, in one of the short stories in Ray Bradbury's The Martian Chronicles— Usher II— the guy re-enacts various Edgar Allen Poe stories.
Also, his short story Usher II, in which all the guests at a party are executed in various gruesome ways (one is stuffed up a chimney by a gorilla) while their robot replicas watch on, thus assuring that none of the guests know what is happening until their own downfall.
In the After Dark series, there are PLENTY of Nightmare Fuel, which often lead me not to read the books at all. As well as the chilling stories, the black and white gruesome illustrations didn't help one bit! One of them involved a school-girl for a school project who learns about how Cod Liver can help halt aging, so she feeds it to her parents... And they start de-evolving toprimates, and then just when you think it was over... HER BABY SISTER who was fed cod earlier, starts to de-evolve too! AAAHHH! Another story, The Bread from Heaven, had an atheist boy called Jacob in an over-religious town (who worship UFOS as miracles from heaven), reject tradition... At the end of the story, he was dissected by the same aliens...
And "Skeleton", a story about a man who developed a phobia of his own skeleton, especially his 'teeth. His freaking teeth''. In the end, he visits a man who is implied to be some sort of inhuman monster and VOLUNTARILY has his skeleton SUCKED OUT OF HIM. His skeleton is then eaten by the monster.
"It was when the jellyfish called you by name..."
"The Small Assassin". It's a short story about a new father who believes his child is fully aware, fully mobile, and killing things; he tries to involve the doctors who treat him as if these are insane ramblings despite mounting evidence that the father is actually right. Eventually the doctor starts to believe the father. The story includes such immortal lines as:
Doctor: See, baby? Something bright, something pretty...
"The Watchers" is probably one of the most terrifying things ever penned. In it, the narrator's friend, having feared animals all his life, finally discovers that animals are actually helpers created by God, whereas bacteria are the real evil creatures. Having discovered this, he starts to be eaten alive before he can tell anyone, takes a boiling-hot shower in a futile attempt to save himself, then wildly drives his car into a ditch. The narrator, seeing his corpse, sets the car on fire, and afterwards is typing out the discovery on his typewriter. The last paragraph or so is a terrifying account of the various germs slowly destroying him from the inside. The story ends with a line of typed gibberish as his eaten-away body fails and presumably falls onto the typewriter.
"Peek a Boo" That's just creepy.
Bradbury's "Kaleidoscope" involves a rocket being punctured by an asteroid, and the entire crew — in spacesuits — blown into space. They had air, but were all helplessly drifting away from each other, and they were discussing which planet or asteroid they would eventually drift into the gravity well of.
"The Veldt", where an animatronic playroom actually came to life and lions devoured the parents of two seemingly indifferent children. What makes the The Veldt all the more nightmarish is that the children weren't even disturbed by their parents' deaths, and that they seemed to have been planning the whole death of their parents all this time. The screams they heard in the playroom turned out to be the screams of the simulated versions of the parents!
"The Whole Town's Sleeping"; a story about a single woman walking home alone in a town terrorized by a murderer called 'The Lonely One'. As if reading through her hand-twistingly tense night-time trek home (through a ravine!) wasn't bad enough, she believes she hears someone following her. She arrives home safe and sound and chastises herself for being so silly as to believe she was being followed, when she hears, in the dark living room behind her, someone clear his throat.
He continues that story in Dandelion Wine where some nearby children watch the police pull a body from the house... then lament that the woman had killed him with a nearby pair of scissors instead of letting him get away because it was just so much fun with a serial killer loose in the town. Thank you Bradbury, for making a happy ending just as disturbing as a bad one.
"The Emissary". A bedridden boy's dog goes out each day to find things for him, and one day leads a young teacher to the house, who befriends him and becomes his tutor. But then she dies unexpectedly, and his dog vanishes for several weeks. Then his dog returns very late one night, covered in deep, worm-ridden dirt, his paws bleeding from days of non-stop digging. And then there's a shadow at the bedroom door, a voice calls his name, and the story ends with "Martin had company".
"Jack in the Box". Gorgeous, happy descriptions of... ohnothat'ssowrong! And the little boy being overjoyed when he finds out he's 'dead'.
"A Sound of Thunder". Who knew a butterfly could cause the Third Reich to win World War 2?
The October Game: A man kills his little daughter at her Halloween party. Then he turns out the lights and passes the body parts around, and meanwhile all the kids are trying to figure out what happened to the little girl and the mom is freaking out and screaming for no one to turn the lights back on. The last line is "... and then, some idiot turned on the lights." And what makes it worse is that the man hasn't gone crazy—his wife, who didn't give him the son he wanted and who adores their only daughter, doesn't love him. He kills the child as punishment for his wife... to take away the thing she loves best in the entire world.
"The Aqueduct": An extremely short story centering around the titular aqueduct which is supposed to deliver water from the North to the South... only the water that finally arrives isn't like regular water at all, but thick and red...
If you were wondering why the water is like that, just before they finished the Aqueduct, the North was torn by a devastating war. That's where it's all coming from...
In a very early and short Bradbury story done for Weird Tales, the dead in a cemetery are communicating to each other via knocking on their caskets. Their topic of conversation? "Mrs. Jones is having her baby today." And it ends with a thin wail rising from one of the caskets...