This is more a case of Gameplay and Story Segregation, in lore, strolling into Stormwind with a demon would get you hanged, but since they can't up and kill a PC like that, it's considered acceptable.
The game does tend to imply that player Warlocks are something of an exception, although asking a guard where the Warlock trainers are will result in them commenting that they're keeping their eye on you. This is backed up when you notice that in Alliance cities, the Warlock trainers tend to look like they're hiding out somewhere, like in Stormwind where they're hanging out in the basement of an inconspicuous tavern, or in Ironforge where about six or seven of them are stuffed into a little, inconspicuous house. This is mostly true for the Horde as well; only in Undercity and Silvermoon do Warlocks practice openly.
Relatedly, none of the Non Player Characters seem to find a Hunter's pet at all odd. You can walk into somebody's house or shop with a miniaturized Tyrannosaurus rex and nobody will bat an eye.
In Neverwinter Nights 2, one character points out that the player's entourage features a combination of characters who'd be unlikely to travel together, like a lawful good human paladin and a neutral part-demon rogue which finds the aura of the former unsettling. And a chaotic evil ranger and neutral evil warlock whose association would cause the aforementioned paladin to actually lose his powers in a pen-and-paper game.
And then there's this exchange:
Grishnak: You're a strange lookin' group. What'dya want? Knight-Captain: ... says the half-orc pirate.
And in the second expansion, Storm of Zehir, the yuan-ti-hating Samarachans don't notice if you have a yuan-ti in your party, with one exception on the Overland Map.
Justified: the player-usable yuan-ti form, the pureblood, is supposed to blend in with standard humanoids.
It also adds the option to have a freaking velociraptor as an animal companion. Nobody comments on it. Ever.
Likewise, in the Baldur's Gate series, most people seem not to notice or comment on the fact that you have Viconia the Dark Elf tagging along in your party, despite Dark Elves still being considered an Always Chaotic Evil monster race that should be attacked on sight at that point in the setting's history. There are a few exceptions, though, and they're the encounters that feel jarring.
In the Crooked Crane tavern, there is a lich hidden behind a secret door. If you lure it out into the main room, no-one will pay any attention, even if it summons a demon. The innkeeper won't even ask you to refrain from having devastating fights with undead mages in his bar.
In the first Neverwinter Nights game NPC's would sometime notice if you ran around with a weapon out or weren't wearing any clothes.
Hilariously averted in A Dance with Rogues with various characters' responses when you talk to them while naked, or the Dhorn in the first chapter running up to you and yelling if you have a weapon out on the streets.
Chrono Trigger has nobody batting an eye at either Frog, who's a giant anthropormorphic frog, or Robo, who's a robot from the far future. Not even Ayla, the resident cave-woman, pays any special attention to Robo. But that's not the worst of it. You can recruit the Evil Overlord Magus later in the game, go back to 600 AD, and talk to the people with Magus, and they'll just say the same thing they always do. Such as expressing relief that the great terror of Magus has been defeated.
Ayla does give special attention to Robo if you bring him with you the first time you go to prehistory, but she just kinda shrugs it off when you're unable to explain what a robot is to her. She also asks if Frog is edible at one point.
Crono's mother has a unique greeting each time you visit her with a new party member in tow. She is somewhat surprised by Frog and Robo but as they are both polite she accepts them without further comment.
In the DS version she thinks Robo is an invention of Lucca's, but does mistake Frog for an actual frog.
Magus also occasionally smirks/giggles at people expressing relief that he's gone. The implication seems to be that while he does look rather strange, he's quite clearly a human and people have a rather exaggerated idea of what he looks like - if they even know at all. Lucca and other 1000 AD scientists can also make robots and they're not out of place in Zeal either. It's possible they were around in 600 AD as well. Frog? Who knows.
Try bringing Magus along on Frog's sidequest, which includes speaking to the ghost of Cyrus, and watch as the latter never even comments on the fact that the Fiendlord, who he actually fought, is among them. Did we mention that this is the same guy who killed him? The only reaction we get from Magus during all this is him shielding himself when the Masamune radiates brightly during a power-up sequence, which is after the conversation itself.
From the characters' point of view, you have the Black Omen. It didn't exist at the start of the game, but in your time travels you have a hand in creating it. Back in your own time, it's now an everyday thing that nobody really pays much attention to, despite being a giant demonic sky palace. There's an old man in Guardia who uses it to tell the weather ("The sun's shining off the Black Omen... it'll be clear today").
To be fair, it's a giant demonic sky palace that's been floating in the sky for all of recorded history and has never done anything other then exist as far as they're concerned.
In Fallout 3, no one bats an eyelid at friendly Super Mutant Fawkes tagging along with you, despite Super Mutants being in the game setting an incredibly feared race of Always Chaotic Evil monsters at war with the human race. This is handwaved with a line of random in-game dialogue in which he suggests that it's because people respect you so much, they trust anyone with you that you aren't shooting yourself. This becomes rather amusing when your character is always in Stealth Mode, and therefore all anyone ever sees is this giant Super Mutant ranting about how much people seem to respect a heat shimmer.
Some NPCs will refuse to work with you or even open fire on you if they see you with Fawkes or Charon the Ghoul.
Also somewhat averted in Fallout 2. Non-human party members are forbidden from entering the highly xenophobic Vault City, and the Deathclaw party member has to wear an all-concealing cloak to avoid being shot on sight. Elsewhere in the game there are towns in which humans, ghouls and non-violent super mutants coexist - nevertheless, humans outside Vault City still seem remarkably blase about you walking around with a ghoul, a super mutant and a robot dog tagging along.
Oddly in Fallout 3 people will shout at you for kicking clutter around ("Be more careful!") and if you pick thing up and move them around ("You're easily amused aren't you?")
In Fallout 2, people will notice you walking around in power armor and make comments like wondering if you're out of some kind of anime.
People will also notice what you're looking at and may comment accordingly. This usually involves cash registers and phrases like "Don't even think about it."
In the Geneforge series, certain types of creations are Barred for being too willful, dangerous, or intelligent. Nobody cares if the player character shapes them, even in the middle of a Shaper stronghold.
In the PS2 game Ōkami, Amaterasu is in the form of a wolf for the entirety of the game. Most people see Amaterasu merely as a wolf, but some spiritually sensitive individuals (such as a particular little girl) can see her colorful markings and hovering holy weapons. But even then, most of the population finds nothing odd about a white wolf wandering the city, buying items from shops, and offering rides on magically created lily pads to passersby. This is partly handwaved by the town's shrine implying white wolves are seen as special, but a few especially thick peasants think she's just a strange dog.
An especially egregious example, courtesy of The Legend of Zelda: Twilight Princess: after beating the boss Blizzeta and before you can collect your Heart Container, Yeto (who's a 20-foot-tall hulking yeti and the boss's husband) bursts through the door to the boss room, and, with a loud roar, shoves Link out of the way to get at Yeta's fallen body — which ordinarily rather observant Exposition Fairy sidekick Midna seems to take no notice of. Indeed, there's later a camera rotation around the couple, and from what we can see Midna's still floating in the exit portal, not even sparing a sideways glance at the two yetis, waiting for Link to get the heart piece and vamoose.
Making this even more jarring is the fact that the game mostly averts this - the townspeople panic and run from you when you're running through town as a wolf.
As well as not allowing you to transform into a wolf where people can see you, as it would freak them out.
But funnily enough, towards the end of the game nobody seems to notice a giant spider-like abomination climbing on the barrier around Hyrule Castle and destroying it. Not that they had noticed the barrier anyway...
And then for the series as a whole, there's stuff like this.
In The Legend Of Zelda Minish Cap, no one seems to mind that Link is running around with what looks like a talking legless mallard on his head while shrinking or growing after jumping onto things.
And then there's The Legend of Zelda: Majora's Mask, where Link can transform (screaming in agony in the process) into a Deku, a Goron and a Zora, soar from one place to another by growing wings & teleporting and alter the flow of time in front of anyone and no one notices.
Skyward Sword has Fi, a holographic being who pops out of Link's sword periodically to give him extremely redundant information. Others can clearly see it, because they turn to look when it appears, but only the robot Scrapper ever acknowledges its existence.
Being very cowardly animal... things, the first Kikwi you encounter will react to Fi by being scared of her and trying to hide.
In Mercenaries: Playground of Destruction, you can cruise through cities and military bases in obviously stolen military hardware ranging from artillery and missile trucks to tanks and helicopters without any particular reaction from soldiers. However, the entire map is a warzone with a daily dose of bombings, shellings, mafia shootings, and the occasional heavy armor offensive. Maybe they just don't care anymore.
The sequel adds a bit of Lampshade Hanging when the citizen of Venezuela, who have been invaded by numerous factions, see your heavily armed Swedish mercenary "Great. Sweden is invading us now!".
In the same vein as the above example, in Just Cause 2, as long as you don't currently have any heat level and aren't in a restricted area, the Panauan soldiers will pay you no heed until you do something to provoke them. This in spite of the fact that you're running around armed to the teeth. And you just massacred 20 of them on the other side of town five minutes ago. And you are currently in the process of sticking triggered explosives to their jeeps.
In the Pokémon games, you can use the legendaries you caught in battle, and no NPC opponent will bat an eyelash. Even Arceus, who is the God of the Pokémon universe.
And in Pokémon Emerald, some of the Frontier Brains use legendaries, which passes without mention. Maybe it's because they use lower tier legendaries, but still...
In Pokémon Colosseum and Pokémon XD you're rescuing Pokemon from bad guys, and they don't seem to care. No one notices the snag machine Wes/Michael has with him either.(save the mooks who steal Michael's machine temporarily in XD)
One mook NPC in the sequel actually does comment on his Pokémon going missing after the battle if you snag it.
And it's more bizarre in HeartGold and SoulSilver, when your primary Pokémon follows you around at all times out of its Pokéball. Yes, even massive, colorful, one-of-a-kind Legendaries.
One trainer who will sometimes call you for a rematch continuously asks if you've seen any legendary birds in your travels - even if a Lugia is flapping its humongous wings right beside you.
Averted in Goldenrod City when you go undercover as a member of Team Rocket. Everyone in the town's dialog will change. However, few of them truly show fear of you, but rather pity or disappointment. They're probably just surprised that anyone would join a crime syndicate that a single 10-year-old kid was able to bring down.
In Pokémon Black 2 and White 2, a sidequest involves finding the dropped Xtransceiver of an idol. After you call him/her enough, you can trade Pokemon with her; s/he will then bring that Pokemon to his/her next show on television. What makes it this trope is that you can trade almost ANY Pokemon to him/her, and see it be on television. Of course, nobody in the audience nor the announcer bats an eye at the God of the Pokemon universe, the legendary dragons of the region, or a gigantic rock dinosaur that can summon sandstorms indoors.
Random people suffering from a monster-induced illness? A seemingly innocent afterschool curricular club, consisting of the daughter of school's main benefactor, that seems to be on an invitation only basis and don't appearto do anything? A group of teens that represent three separate subcultures and stand out like a sore thumb in the middle of a normal Japanese city? Three transfer students being integrated into one class? Anyone outside of S.E.E.S. The Kirijo Group, Strega and Ryoji in Persona3 is mostly oblivious to what is really going on in Port Island.
In Dragon Quest V, someone in the Dark World comments, "Did you come from the surface...? No, that's impossible." Come on—if you saw someone wearing a shining golden crown, with a golden breastplate, royal cloak and a dragon-shaped staff that glows, as well as his two kids, one of whom is in the armor of the Legendary Hero, don't you think that he might be slightly more powerful than average?
In the Kingdom Hearts series, no-one from any of the worlds seems to worry about how different the main characters are, which is especially weird in the Pirates of the Caribbean world, which is the closest to 'the real world' the game gets. One would expect Will or Elizabeth to be a little surprised to see a talking wizard duck, but no one seems to care. And the main characters are also so brightly colored in comparison with the rest of the world! Interestingly Sora and his friends do comment that this world is weird for some reason they can't quite put their finger on. The only possible justification is that once Will and Elizabeth got into the whole zombie pirates thing, accepting a talking wizard duck wasn't so bad in comparison, but it still doesn't account for the flatout difference in art styles.
Which is interesting because some worlds have Sora, Donald and Goofy transform or wear different costumes to fit in (Pride Lands, Atlantica, Halloween Town), but most of them don't. It could be explained by the Rule of Cool, but how cool would it be if Sora dressed as a pirate?
Oddly enough, King Triton actually DOES call Sora out on being from another world. But only because he doesn't seem to know how to swim right. Goofy and Donald get no such remarks.
In Kingdom Hearts 358/2 Days, Roxas is typically supposed to avoid being seen by the inhabitants of the worlds he goes to on missions, but no one seems to find his appearance or behavior at all strange when they see him, nor do they see the similarity between him and Sora.
Your eyes deceive you. Magic Carpet knows that Roxas is Sora, because it doesn't rely on sight. Everybody else relies too much on sight. Besides, what have we ever seen of Phil that would indicate he'd even care enough to notice the similarities?
The actual justification in Days for no one connecting the Sora-Roxas dots is that this was the year Sora was being repieced together mentally. Everyone had forgotten about Sora while his chain of memories was reforged.
In another example of 'real-worldness', Kingdom Hearts 3D [Dream Drop Distance] has Sora and Riku visit The Grid from TRON: Legacy, with no-one ever commenting on the fact that the pair look somewhat different. It could possibly be handwaved by the fact that it's all taking place in a computer, and there are all sorts of different programs, but still...
And don't forget about those Pokémon-like creatures that hang around them....
In the Fatal Frame series, characters will often have an opinion on furniture and foliage, but refuse to comment at all about things like trussed-up corpses lying on the floor, apparitions in the kitchen, or dolls with heads that move and hair that grows. They also rarely show any surprise or disbelief when they learn that ghosts exist.
Justified in that Miku (first and third game) and Mayu (second game) were born with sixth senses. Miku's brother also has it (but is promptly kidnapped) and Mayu's twin sister Mio has a weaker version.
In Jak II: Renegade you can steal vehicles right under the Krimzon Guard's nose and no one will comment on it except for the poor soul who just got his zoomer stolen. No one will move a finger to help him either. Also, the Krimzon Guard is supposed to be looking for you everywhere but you can stand in front of one and be completely safe. It's only if you harm one of them when they actually notice you.
There is only one instance in the whole series where someone actually reacts to your Talking AnimalSidekick, and it's little more than just the eyes widening for about two seconds. However, considering that there's at least one other Talking Animal in the series (more if you count Lurkers), it may actually be pretty common in that world.
Lampshaded in Albion, in which an evil corporation is attempting to terraform an inhabited alien planet by claiming to its workers (who do not interact directly with the planet, and are merely crewing a gianted automated factory ship doing the work) that the planet is actually just a lifeless ball of dirt. You can talk your way out of the final battle by telling The Dragon that (paraphrasing) "One of my party members is a 7-foot-tall anthropomorphic cat. How do you explain that?".
Scarface: The World is Yours. People will react to you waving a gun around and shooting gang members. Once you put the gun away, however, everything is just fine. This is Tony Montana. Would you say anything?
Averted in Assassin's Creed I; anytime you climb up a wall in plain sight, people will comment on it. Some might say that the game also plays the trope straight with respect to the arsenal Altaďr carries around with him, but it wasn't all that remarkable for someone to go armed in the 12th-century holy land, even if Altaďr does carry several more blades than are strictly necessary.
People still assume The Guards Must Be Crazy when the aforementioned clearly and visibly heavily-armed Altair can pretend to be a monk and get away with it.
Listening to people's comments when they notice Altair or Ezio climbing a wall shows that, while some think it's really strange, others assume you're just exercising.
It gets even more ridiculous in Brotherhood, when Ezio (in ancient armor and armed to the teeth no less) can pull any civilian off a horse to steal it from them, usually running over them and several other pedestrians in the process, without nearby guards even batting an eyelash. But if you tear down a wanted poster within sight of the guards, oh boy...
The games in the series also feature the Leap of Faith - jumping off tall buildings or other high places in a very stylish manner and landing in hidings spots like carts of hay, without anyone ever paying attention to the fact that a man just fell from the sky and landed in a pile of hay. Best explained by the Rule of Cool.
People panic and back away if Ezio attacks civilians, but anyone but Ezio dies on contact with water, so on docks it's pretty easy to wander around killing people without anyone noticing.
In Assassin's Creed III's Brazil mission, the amorous couples don't seem to even notice when Desmond gets into punch-ups with guards.
Both averted and played straight in Golden Sun: The Lost Age... in the same town, even. Upon his arrival in Madra, Piers is promptly associated with the pirates who recently ransacked the place, arrested, and the talk of the town for being a foreigner and an oddity. Once you've rescued him and added him to your group, you can return to Madra and meet Karst there. Nobody comments on her. Apparently a scantily-dressedCute Monster Girl isn't nearly as weird as a guy with blue hair.
In fact, nobody ever comments on the Mars Clan having double-pointed ears, colorful skin, scales, Red Eyes, Take Warning, and bizarre hair (though apparently normal people in the 'verse do rarely have unusual hair colors or styles, usually a visual cue that they're Adepts). Even your own party members don't seem to think them unusual, save for an offhand comment about Karst's clothing.
In Star Wars Knights Of The Old Republic, once you rescue Jedi Bastila you can wander around the Sith-patrolled streets of Taris waving her lightsaber around, and nobody so much looks in your direction, despite her being Number One on the Sith's Most Wanted List.
Also applies to running about in Jedi robes with a blue lightsaber at the Sith Academy on Korribannote though that actually gets a passing explanation — the Academy gets a steady influx of Jedi that has fallen to the Dark Side., and to running about with a lightsaber at all in the Jedi-hating settlement on Dantooine in the sequel.
First noted when Mami is introducing Fou-lu as her war-injured cousin "Ryong". This would be plausible...except for the fact that Fou-lu has red horns on his head and pointed ears. Fou-lu speaks in Ye Olde Butcherede Englishe. In one of the few villages not inhabited by Petting Zoo People, the only person who brings this up is the landlord who eventually ends up selling Fou-lu and Mami out, leading to Mami's death and Fou-lu's Roaring Rampageof Revenge.
The only bit of lampshading that is done at all on this in the game, in fact, is Mami excusing Fou-lu's odd speech and general lack of familiarity with the village or anything modern as being essentially the result of a head injury. This is even after Fou-lu dispatches a purported volcano god.
The manga doesn't even bother with the "head injury" lampshading, but does imply that people in Sonne do cotton on that Fou-lu isn't quite a normal feller.
What happens with Ryu when he enters Sonne actually manages to make the above look completely plausible in comparison. He's called "Ryong", is greeted as if he's actively returning, and otherwise treated as if he were in fact his other half...despite the fact Ryu and Fou-lu look noticeably different. You'd think the fact that Ryu has blue hair rather than white, has a distinct lack of horns, and doesn't speak in Ye Olde Butcherede Englishe would be a clue. The only plausible explanation is that the backwater farming village of Sonne is secretly a village full of psychics who can all see that Ryu and Fou-lu are part of the same Literal Split Personality.
In Brutal Legend, Eddie doesn't bat an eye at anything in the age of metal.
Helps that he thinks that the world is nothing but pure awesome.
Generally averted in The Darkness, where everybody reacts properly when you manifest The Darkness (civilians panic and flee, and (Suicidal Overconfidence aside) Mooks scream out loud about being attacked by monsters). However, Captain Shrote doesn't seem at all fazed by The Darkness and mocks you about it when you confront him and Uncle Paulie face-to-face at the end of Chapter 1. He even works out how to neutralize your powers in the finale of Chapter 4.
Both averted and played straight in Star Ocean: The Second Story. No one on Expel seems to bat an eye on the fact that Rena has elf's ears (because she's actually a Nedian, not an Expelian), or that Ashton has dragons on his back, or that Opera and Ernest have three eyes; but Claude, with his unusual clothing, turns heads.
The series as a whole tends to do this. Your space-age heros wander pre-industrial worlds where nobody notices their bizarre ears, magical devices, lack of Petting Zoo People appendages, and total ignorance of basic local philosophical concepts, events, politics, and geography, but everyone always immediately notices their machine-made synthetic-fabric clothes.
The first Star Ocean has this as well. The two Earth humans in your party don't really notice anything strange, but it can be explained by them having found and seen a lot of different planets with different types of people. They pretty casually explain to the heroes that they don't have tails, and nobody on the human Star ship seems to notice that THEY do, but it still might be due to there being a wide variety of people with traits like that.
Later, it's averted when they travel back in time on planet Roak and Ilia hides and asks for new clothes to fit in, but then played straight afterwards in that nobody on Roak seems to notice she (and Ronixis) don't have tails (and for some reason their clothes don't even have holes for them despite coming from Roak).
While most of your party-members in Mass Effect 1 and its sequel are perfectly normal members of the standard galactic races, one of your ME2 party members, Legion, is a member of a race best known for a genocidal war or two, and a recent devastating attack against the center of galactic government, yet no-one, including a Citadel security guard bragging about the anti-Geth security, finds this the slightest bit odd. The guard simply assumes that Legion is a robotic assistant. You can see Legion twitching. "Geth don't infiltrate." said the Geth Infiltrator. "Geth don't intentionally infiltrate," he amends a moment later due to the aforementioned stupidity. Acknowledged by Anderson, who comments that Shepard's "trophy-bot" hasn't caused a stampede.
No one bats an eye at Shepard, who carries half a dozen weapons (one with radiological markings) on their back, in top-of-the-line body armour, with two other people similarly armed. On the Citadel. Even though s/he's the first human specter, has saved the galaxy a bunch of times, came back from the dead, few people recognizes him/her.
Even after you recruit Archangel (Garrus), you can take him around Omega, the space station where he managed to unite the warring mercenary factions that are in charge solely due to hatred for him, with nobody commenting. Granted, he's thought to be dead, but no one notices that he's wearing the same armor as Archangel. Justified though, as only no-one outside of his group of True Companions knew what he actually looked like and the criminals who did end up coming face-to-face with him, rarely survived the encounter.
Jack is a wanted criminal on Ilium, complete with an unreasonably large billboard announcing it, yet no one makes any attempts to arrest her. This may have something to do with the fact that she's hanging around the aforementioned heavily-armed undead Commander Shepard, and Ilium has legalized everything but murder.
Mass Effect 3 DLC gets you Javik, the sole survivor of a race thought to be dead fifty thousand years ago, and who are generally worshipped at near god levels (actual god levels by one race). Other than one cut scene, nobody outside of your party tends to notice him. Of course, Shepard is well-known throughout the Galaxy for attracting these types of people, so it's implied that people have become a little desensetised to the sight of a strange alien in their team;
However, a Hanar will recognize him and go all "I am not worthy!" on him. Later, a few Citadel civilians will approach Jaavik with awe, so it could just be that Shepard and Jaavik are too intimidating to be approachable.
After EDI gains a Fembot body to serve as her physical avatar, Shepard expresses surprise that Joker managed to get her onto the Citadel. Joker explains that they've been maintaining the lie that she's his "Personal Mobility Mech", after discovering that because of his Vrolik's Syndrome, he's actually legally entitled to have one with him at all times.
Usually played straight in Sam & Max: Freelance Police, with characters only making passing references to the eponymous characters being animals. Sometimes averted for laughs.
"What was in there, Sam?"
"Apparently a bunch of temp workers who have never seen a six-foot-tall dog looking through their window before."
Sam & Max: The Devil's Playhouse: Nobody also cares when a spaceship crewed by alien gorillas lands on their street or when Max starts teleporting all over the place.
In Noctropolis, the only people who seem able to process that the two people in front of them are the local superheroes are the local supervillains.
Subverted in Final Fantasy XIII-2: Most NPCs do react to Mog, and they'll even come running and crowd around when you use some of his... weirder powers.
Unless you use its power very close to a person, then the people will start to run away. Considering what we see what happens when you use it on the people in the dream version of Noel's world is quite understandable...
A disguised Mercer in Prototype can drop out of the sky hard enough to leave an impact crater in asphalt and then stroll around like nothing happened. Even those who briefly noted it will quickly forget by the time he does something else incredibly bizarre. It takes a sustained abuse of powers before his cover is blown.
Averted in the Fable games. People actually freak out if you pull out a weapon in a crowded area.
Slightly similar to the Jak II example above, in Oblivion you can feel free to either break in and steal, or simply pickpocket an Imperial Guards' suit of armor, then equip it and talk to the Imperial Guards, who still refer to you as "citizen". Presumably similar situations can occur with other types of armor that your character shouldn't legitimately be wearing yet.
Averted in Morrowind, where wearing certain types of armor, for example the holy armor of the Ordinators, will get you butchered by angry fanatics.
Averted in Custom Robo Arena. At first the protagonist and his friends are dismissed as they bunch of kids they honestly are, but as your fame grows people start to recognize you on sight. By the Playable Epilogue you're a household name and nearly everyone is in awe of you.
Commenter: I had a game where a kitten killed a cyclops, but beyond that my experience mirrors yours.
Another Commenter:This is the point where I'd normally call bullshit, but having (un)successfully ground no less than ten forts into destruction and abandoning three more to boredom after guaranteeing success I 100% believe that this happened in your game.
Taken to the extreme when a spammer started posting some gruesome pictures. The discussions simply went on.
Commenter: I'm slightly terrified by how utterly unfazed everyone is...
Another Commenter: This from the woman who just explained in another thread how she drops her children into a glass enclosed splatting chamber in her dining room. Well, not her children, her dwarves' children. But still, she's terrified by us?
Hilariously averted when DF 2012 and the new necromancy system were in development:
Development Log: In bug news, the zombies in a necromancer's tower became suspicious after the necromancer failed to age, and he fled into the hills.
In The Saboteur, you can climb to the tallest chimney you can find which has a group of nazi soldiers nearby, and then just stand there having a smoke like a boss. Nobody gives a royal damn. Now walk a step or two so you jump down and grab the ledge where you were just standing, while the soldiers keep looking at you. Hilarity Ensues.
Lampshaded in Shadow Hearts: From the New World. Relatively normal Johnny is generally surprised and unnerved by all the bizarre things everyone else seems to shrug off. When he meets a giant, anthropomorphic, talking cat who also happens to be a Chicago mob boss, it becomes too much. Mao, the cat, asks, "what's so unusual about a talking cat these days, anyway," but Johnny protests that it is unusual and looks to the party for confirmation. When they don't back him up, he finally comes to a different conclusion:
Johnny: Wait... is it me? Am I a weirdo?
In the original PS1Resident Evil Barry will a one point walk into a room after Jill has just killed a giant snake, and its melting remains are still a smear on the floor and ask "Jill, have you found anything interesting?"
In Lego Harry Potter Years 1-4, you can utilize a cauldron of Polyjuice Potion to turn into any character that you've unlocked so far. Nobody at Hogwarts seems to react any differently if you've suddenly turned into Lord Voldemort.
The Elder Scrolls V: Skyrim: Nothing weird about that guy walking around with a ghost who talks loudly about how they are off to murder the Emperor and how they both work for the Dark Brotherhood. Even if said ghost and its master are currently walking through a town populated entirely by said Emperor's Praetorian Guard.
Averted with the Thieves Guild armor, which many guards will remark on and say they recognize. This leads to the Fridge Logic of just why a thieves guild would have a uniform that is instantaneously recognizable.
It's a calling card that makes capers all the more daring when you're rubbing your affiliation in the guard's faces the whole time.
Another reason is that the Guild has fallen on hard times, (although you can change this), so many Guards outside of Riften honestly don't take the Guild seriously at all. It also seems that the Guard are apathetic and long as they don't see you commit a crime, you could walk around naked in a chef's hat for all they care.
Skyrim's generally pretty good about averting it, actually (possibly in response to Oblivion being mocked relentlessly for its Artificial Atmospheric Actions and Talking to Himself). It's also averted with standard armors. For instance, guards will compliment you on your fashion sense should you be wearing ebony armor.
Also averted when a random dragon encounter happens in town. When you kill it and absorb its soul, the guards will react with awe.
Also also averted when you use Shouts in town. "The Thu'um! S/he summons the the Thu'um!" They'll also tell you to cut it out if you do it too often.
One your way to the Rank 5 fight in No More Heroes, a trail of blood pools leads you to a dead body (which also leads you to a path to the same fight) and everybody just goes on with their business. Possibly justified, considering what kind of environment Santa Destroy is.
Played straight in Street Fighter X Tekken's Rufus vs. Bob's trailer, when Ryu and Ken eat ramen together and don't seem to even notice Rufus flying past them.
Definitely justified. They're Street Fighter characters, and street fights are common enough that they don't really care when one happens around them.
There are also subversions. People are watching the fights excitedly (some background characters play it straight by continuing to do what they do, as with the Street Fighter X Tekken example above), but nobody seems to notice the fighters throwing fireballs, BREATHING fire, shooting electricity, flying, stretching limbs, possibly not even being human, generating sonic booms or dragging characters through the 16 Buddhist hells in a flash of light (and possibly killing them, if a match is ended this way in Street Fighter IV, the K.O. sign doesn't pop up). They just watch as if its a normal fight.
This also happens in Tekken. A MUCH more realistic fighting game, but some of the backgrounds are filled with people who don't much care or probably even notice there's a fight going on.
And if the audience is watching, they don't even really bat an eye when the fighters include robots, demons, animals and monsters, and when supposedly normal humans use eye beams, swords and even guns in what is supposedly a martial arts tournament...
In the console intro movie of Tekken Tag Tournament 2, Ogre bursts out of the ground and interrupts a tournament fight (between normal humans), poses menacingly and breathes fire around the arena. The audience cheers! Shouldn't they be running for their lives?
Which is then followed by an angelic woman glowing with holy radiance swooping down and proceeding to engage in a Beam-O-War with Ogre. The crowd continues to eat it up, the risk of being caught in the crossfire between two supernatural entities never registering. To a lesser extent, the arcade intro similarly has no one batting an eyelash at Alisa or a some forty years younger Heihachi.
Mega Man Star Force: you would be astounded how many waveholes are located out in the open and/or within five feet of someone facing toward it. More than once you can Wave Change directly in front of someone and they don't even notice the kid vanishing into thin air. The one NPC in the first game who spots Luna vanishing when she turns into Queen Ophiuca actually feels jarring because of this.
Double subverted in Xenoblade. After Fiora rejoins your party, you can bring them back to their hometown. NPCs will actually comment on how surprised and relieved they are to see them still alive, but don't seem to notice the fact that she's been turned into a Machina.
Space Station 13: Blood is a very common occurrence on the station, and expect no one to care that every inch of medbay is covered blood, even on the servers that are much more RP heavy.
In Dragon Age: Origins, when playing as a mage, you quickly learn two things regarding Blood Magic: It is supposedly inherently evil, making it an officially shunned practice, and seriously lacking in the subtlety department, as even the most simple of blood magics invokes Overdrawn at the Blood Bank. Now become a blood mage and notice that even the biggest nay-sayers won't as much as react on your reckless display and blatant disregard for the dangers of such magic. Hell, you can even turn your resident White Mage, who spends most of her dialogues sternly lecturing you and other users about the inherent dangers of Blood Magic, into one and she will never comment on the hipocrisy!
In the expansion Dragon Age: Origins – Awakening nobody seems surprised to see Kristoff’s decaying body talking and walking around. It's adverted otherwise, when NPCs will identify you as a mage/elf/dwarf/human/Grey Warden and react accordingly.
In Dragon Age II apostate Hawke can walk around in robes and with a staff without getting arrested, even through being a mage outside of the Circle is illegal.
Justified in that the mercenary camp/smuggling ring has connections, and hid Hawke's abilities despite knowing of them (thanks, Gamlen). By the time Knight-Commander Meredith noticed Hawke, he was already a local legend and a bit of The Dreaded. Becoming the Champion made Hawke untouchable, and then she attempted to sway him on her side. Only until Meredith invoked the Right of Annulment does she want to kill (not arrest, but kill) Hawke, but only if Hawke sides with the mages.
In Persona 4 Arena, Teddie introduces Labrys, a robotic girl with a giant battleaxe to the group. How does Chie react?
In the first stage of Metal Slug X, there are a pair of background NPCs who keep on chatting calmly even as you start gunning down mooks.
In Ghost Trick, characters who are unaware of Sissel's existence don't really notice when objects move about on their own, just treating it as a coincidence if and when they do notice. Which makes it even more of a shock when Beauty addresses you directly thanks to her "sixth sense", and downright terrifying if Yomiel spots you, causing a Non Standardgame Over in the process. To be fair, most of the objects that move around are objects that can naturally move around on their own, and often do in real life. Also, a lot of the time it's justified by the fact that the characters are experiencing events that cause them to not really have the time to ponder why an object has somehow moved. In such events, people would either not notice or just pass the cause off as something they didn't see and concentrate on the life or death situations.
In Project X Zone, when Kurt and Riela join the party, Reila hesitantly shows off her Valkyria form. Instead of the reverence or persecution this gets her in her homeworld, the dimension-hopping group's reaction ranges from "Neat trick" to a resounding "Meh". The most respect her situation gets is Frank West having his picture of her classified as Drama.
Star Trek Online has at least one mission ("Everything Old is New") where you go back in time to 2265, the Star Trek: The Original Series era. Nobody bats an eyelash at your 25th century weapons and body armor (apart from Scotty, who offhandedly remarks that your uniform is funny-looking), or if you or your bridge officers are members of species not known to have been encountered at the time.
In Hatoful Boyfriend civilization is run by uplifted birds, to the point where characters use words like "everybirdie" quite casually. This is normal. Everyone's grown up with that system. In the manga the setting is established as an all-boys' school (with the Token Human also being the token girl). Yuuya is given many presents on their equivalent to Valentine's Day and Okosan casually mentions having laid an egg. The only character to bat an eye is the out-of-country transfer student, Sakuya.
Evil Genius: Many things will draw the attention of agents - Freaks, armed military minions, body bags. Somehow, your henchmen - including shirtless voodoo priests, ronin, and hulking doctors with tribal tattoos juggling cleavers - do not.