Referenced by Dickens in his account of his journey to America, American Notes. A few days into his trip over the seas, he's utterly bored to the point that "if Neptune himself had walked in, with a toasted shark on his trident, I should have looked upon the event as one of the very commonest everyday occurrences".
Among many others in Animorphs, the commercial scene in the third book.
Lampshaded in The Heroes of Olympus when Percy runs through traffic with "June" Juno in Son of Neptune, most of the drivers, "just swerved and looked irritated, as if they had to deal with a lot of ratty teenagers carrying old hippie women across the freeway." It's The Mist again.
The character of Clara in The House of the Spirits has telekinesis. It's mentioned that when she was young and people came over for dinner her family worked out a system to prevent people from noticing plates and saltshakers randomly rising into the air. When she's older, her husband and children are utterly unfazed by seeing her sitting in a chair that's zooming around the room and playing the piano with the cover closed.
It's at least partially a Magic Realism novel, so that's par for the course.
The Cullens and Hales in Twilight. For the most part they don't claim to be related by blood, but they're all very pale, young-looking, hot (specifically, they are all breathtakingly beautiful and snow white, with gold—not brown—eyes) people whom Muggles (with the exception of Bella) have a tendency to avoid, but no one seems to find it strange.
To be fair, they do find them strange. They simply have stopped caring way before Bella came to the town.
In the first book, Edward stopped a runaway van in the school parking lot from hitting Bella, using his bare hands. The book specifically says that a "sea of faces" in the parking lot turned to look. But nobody except Bella noticed anything unusual, including the van driver.
Eclipse alludes to a vast amount of death and destruction going on in Seattle thanks to the newborn army, and The Short Second Life of Bree Tanner confirms that it reached levels where one would think national security would take interest (especially seeing as the timeline set it at not long after 9/11). While some people are mildly concerned, most of the citizens of Forks pay little attention to the fact that countless people are dying or disappearing, and the streets are filled with fires and car wrecks (and, oh yeah, an entire ferryboat of people die). In Breaking Dawn, no one at all comments on the incident. Of course, it could also be that it's a result of Bella telling the story and being too disturbingly self-centered to care.
In New Moon, Charlie doesn't seem to notice Bella coming home with stitches and a huge bandage around her arm. She tries to handwave it as normal for her to come home with injuries from her clumsiness, but one would think such a huge cut would get some attention from the Forks Police Chief.
Discworld has the Librarian of Unseen University, who has been an orang-utan since the second book. It's gotten to the point that if someone were to tell the faculty about the 300-pound ape wandering around the campus, they would ask the Librarian if he'd seen it.
In Wyrd Sisters, it's said that there's so much magic in the Ramtop Mountains that weird things are always happening. When the citizens of Lancre hear about or see something that would be regarded as an omen anywhere else (like geese walking backwards, moving trees, or two-headed calves being born), they just roll their eyes and say to themselves "Not another bloody portent." It's only when the portents stop happening that people get worried.
In Unseen Academicals, everyone seems more focused on the results of the football game than the floating, glowing golden woman. Admittedly, it was a pretty close game, and weird manifestations of gods really do happen a lot. In The Discworld Almanak we're told that the God of Astrology regularly visits the publishers with the rays of the sun coming out of his head, a belt of stars, one foot resting on a lion and the other on a crocodile, and carrying nine daggers in one hand and the crescent moon in the other. The only reason he turns heads when walking through Ankh-Morpork is that the lion moves faster than the crocodile.
Justified in The Eyes of Kid Midas, incidentally going one step creepier than a Weirdness Censor. Whenever the eponymous Reality Warper makes a change, everyone else's memories change to match, and furthermore what changed will seem normal to them. (There's a memorable scene where a teacher has it pointed out that one of his students is four inches tall, and he ponders it, says he never noticed, and asks why it's being brought up.)
Built up in David Weber's Safehold book, Off Armageddon Reef. King Haarahld and Prince Cayleb each work out that seijin Merlin Athrawes is much more than the already extraordinary person he appears. So much so, that when Merlin has to expose some of his full ability to deliver a warning from Cayleb to Haarahld in a single night (when normal methods would have taken two weeks) neither are especially shocked. When Haarahld in particular fails to react to Merlin's sudden appearance, Merlin ponders if their family has some kind of genetic defect since something is clearly wrong with their "Fight or Flight" instincts.
The second book, By Schism Rent Asunder, reveals the reason that Haarahld was less than shocked was because he knew about the falsehood of the Church of God Awaiting all along, and suspected Merlin to be the second of two known gambits to overthrow it.
In John T Sladek's satire Roderick, none of Roderick's schoolteachers believe he's a robot. They all assume he's a disabled kid in a mobility suit who's fantasizing about being a robot.
Justified in the Belgariad, no one thinks Garion's BFS is at all out of place, because the Orb attached to the pommel gives it a built in Weirdness Censor that makes people ignore it.
This principle is so well understood in The Hitchhiker's Guide to the Galaxy universe that it has been weaponized as the SEP (Someone Else's Problem) field. If something is so unusual that it doesn't make any sense for it to be there, people will just pretend it isn't.
Also from Douglas Adams, in The Long Dark Teatime Of The Soul, Thor the Thunder God has a spectacular fight with a huge golden eagle in a Primrose Hill neighborhood, in which thunderbolts and hammers are tossed and the opponents Roof Hop between the tops of lampposts. When it's over, an elderly lady who'd paused under one of the lampposts simply resumes her dog's evening walk, content to move on without comment now that the ruckus isn't in her way.
Justified in the Nightside series, where overtly gawking at the bizarre sights and extraordinary characters on the streets only marks you out as a tourist.
In the Earthsea Trilogy Roke Island is home to the School of Magic which results in all sorts of bizarre occurrences such as flying houses, people transforming into an animal (or vice versa), etc. The locals are used to this and barely give a second glance.
In the Tortall Universe, Song of the Lioness has Alanna followed around and helped by a supernatural cat. He's black with startling purple eyes, talks, does magic, is generally very intelligent and knowing, and does such very uncatlike things as traveling across the world and joining his mistress in battle. People notice his eyes, and are startled the first time he speaks to them, but largely his strangeness is not remarked upon, although such cats are not otherwise seen in the story. Even Alanna, though she once wonders if he's a god or something, quickly concludes that he's just a cat.
Four hundred years prior, in Provost's Dogs, he helped a young constable named Beka and everyone noticed that he was strange. Other constables joked that he should get pay, like the scent hounds, for taking shifts. He's accepted, but Beka's friends speculate about him and actually figure out what he is. This discrepancy can partly be attributed to Tamora Pierce growing and changing significantly as a writer in the time between the two series, but there's some in-universe reasoning too: with Beka, the cat was far more flashy and willing to use strange abilities, while with Alanna he usually kept to advice and standing guard; he spoke more to Beka's friends than Alanna's, and in Beka's time the gods forbid him to visit the mortal world for hundreds of years thanks to his interference. He seems to have learned to be less flashy. And since the end of Provost's Dogs has him spelling George so he doesn't remember the description of Beka's magic companion, he may just be using magic to keep too much attention from heading his way.
According to The Zombie Survival Guide the Romans considered the zombies just like this: a (creepy) problem requiring a practical solution (namely, cut the head of the monster and burn the whole thing as soon as they are all beheaded). They also wrote their own manual to dispatch zombies, that allowed them to neutralize all outbreaks in their territories before they became actual threats (the one that did was outside of their territories and prompted both the building of Hadrian's Wall and the creation of the Roman manual).
This trope was also invoked near the end of the Roman empire, where an old, retired legionnaire saves a woman and child by walking up, decapitating the zombie and walking away.
In The Dresden Files, the protagonist at one point reveals himself to his True Companions to be alive despite having seemed dead for over a year. Absolutely nobody is surprised by this, though they do take the time to confirm its him first. At least one person even figures it out, figures out what he's doing, and comes to help without even being told it's him. They, too, are completely nonchalant about it.
And in the book after that, when the protagonist has (seemingly) returned to being dead, his apprentice in magic is not only completely unsurprised when he comes back to life, but actually prepared for it by setting aside a room for him in her apartment.
This trope is justified, given that said companions are fully aware of the supernatural world and how much weird crap goes on around the protagonist.
In the Principia Discordia, in the story of how the Honest Book of Truth was discovered, Lord Omar is told by a servant of Eris to go to a sacred mound and dig up the book there. He digs for five days and five nights and finds no book, so he decides to take a rest, using a giant golden treasure chest he found on the first day as a pillow.
...a stranger to the boggies of the Bag Eye, a stranger they had understandably overlooked because of his rather ordinary black cape, black chain mail, black mace, black dirk, and perfectly ordinary glowing red fires where his eyes should have been.
In his book The Age of ReasonThomas Paine wrote that, assuming it happened, the rising of the dead described in the Gospel of Matthew at Jesus' death must have been this, since no one appears to have written down any other accounts. Matthew is also the only Gospel that mentions it. Nor does it say what happened afterward-did they return home to their families, attempt to reclaim their property, or just go back into their graves quietly?
Another noteworthy instance from The Bible is the account of Balaam and his donkey. You'd think a donkey asking you why you're hitting it in your own language would at least throw you off a little, but the story just has Balaam answer the donkey like it'd always been speaking to him.
In one scene in Relativity, two of the superheroes board an elevator. At the second floor, a man in a suit joins them, but he's apparently too tired to notice who he's riding with. He casually gets out at the third floor.
In Harry Potter, students raised among muggles (for example, Harry himself) are taken by surprise at the many magical-related things that go on around them. Meanwhile, most witches and wizards don't even look up when they see people with strange hair colors, students getting changed into badgers, or people visiting the hospital wing as cat-human hybrids. On the flipside, students raised in the magical community are often amazed by things like aqua lungs or stationary pictures, which muggle-raised students find perfectly normal.
When Harry stays with the Weasleys for the first time, he finds it strange that the sounds of explosions coming from Fred and George's room is considered normal.