- Evangelion 303: Asuka feels like this often due to being -in her opinion- Surrounded by Idiots and weirdoes.
- In Equestria: A History Revealed, this trope is somewhat juxtaposed in that the only logical pony around seems to be Crazy Larry. This is given that he often points out the inaccuracies and Insane Troll Logic of the text sometimes, and while still somewhat crazy himself, he's still leaps and bounds more sane than the Lemony Narrator.
- Honor Trip: Poor Kaji, forced to constantly be in close proximity to Hagala, Hufeh, Ignai, and Kataba.
- Harry Potter in the fanfic How Hogwarts Became A Nudist Colony. After a battle with Voldemort, Harry returns to Hogwarts only to find that it's now a nudist colony:
Dumbledore: You may have noticed a few changes around school?
Harry: A FEW! WHAT THE BLOODY HELL HAPPENED WHILE I WAS AWAY? WHERE'S EVERYONE'S BLOODY CLOTHING? ARE YOU ALL MAD!?
Ron: 'arry, that's just not polite.
- In the Harry Potter fanfic Harry Potter and the Methods of Rationality:
You're giving me a time machine to treat my sleep disorder.
You're giving me a TIME MACHINE to treat my SLEEP DISORDER.
YOU'RE GIVING ME A TIME MACHINE IN ORDER TO TREAT MY SLEEP DISORDER.
"Ehehehehhheheh..." Harry's mouth said. He was now holding the necklace away from him as though it were a live bomb. Well, no, not as if it were a live bomb, that didn't begin to describe the severity of the situation. Harry held the necklace away from him as though it were a time machine.
- Played With, in that the rest of the characters are perfectly normal, and Harry is simply significantly more sane than the average person. (Most of the time, anyway.)
- By Word of God, characters intended to meet this trope include Harry, Hermione, Professor McGonagall, Professor Quirrell, Draco, Neville, Daphne Greengrass, Susan Bones, Mad-Eye Moody, Amelia Bones, and Fawkes. Note that in many cases, these are the same characters whose madness is being contrasted against.
- In the Disgaea fanfic Disgaea Jewel of the gods Adell is this, due to Laharl and Mao often arguing all the time, or being crazy.
- Mao is this when Laharl and Adell are being too Hot-Blooded.
- In the South Park fanfic Etruscan Philosophy, by Gariand, Stan plays this role to the hilt:
For what seemed like the millionth time, Stan was forced to act as peacemaker. "Cartman, shut up. Kyle, calm down. Kenny, this isn't funny." He pinched the bridge of his nose.
- Subverted in Shinji And Warhammer 40 K, where Ritsuko's attempts to make sense of the increasingly physics-breaking powers Shinji develops from the AT-field and the other incredibly odd events happening around her.....end up driving her insane.
- Played straight in Bagenders with Legolas (and possibly Sam), Aragorn being somewhat neurotic, Frodo being insane, Gandalf being a Dirty Old Man, as are Merry and Pippin, Gimli is rarely seen, but has installed anti hobbit defence mechanisms in his room.
- Of course knowing the crap that Merry, Pippin, and Frodo do that's an example of Properly Paranoid.
- Zuko in the Avatar: The Last Airbender fanfic The Boiling Rock definitely fits it. If he's not breaking the Fourth Wall, he's mentioning how the story is nothing but a world of madness that he is trapped in.
- Sora in Kingdom Hearts The Short and Honest Version fanfic and it's sequel. To Quote said Character.
SORA: AM I THE ONLY ONE WHO SEES THE MASSIVE ORB OF PURE EVIL ABOVE US RIGHT NOW? AND HOW THE HELL DO YOU HAVE AN ANY IDEA WHAT THE FUCK IS GOING ON? I'M THE ONE WHOSE BEEN HAVING PROPHETIC, MATRIX-LIKE DREAMS!
- In Oh God, Not again! Neville, out of all people, is the most sane character in the entire cast.
- In almost any Sonic the Hedgehog fanfic, that stars Team Chaotix, Espio will be this.
- Hitsugaya in Uninvited Guests is the only one who doesn't operate under Insane Troll Logic or alcoholic madness. Well, before he snapped that is.
- In the Mass Effect fanfic Inglorious Bosh'tets, Tali'Zorah has the unenviable task of trying to manage a crew of idiotic and insane Quarians, all of whom blame her for pretty much everything.
- In the Death Note fanfic I Won't Say Light Yagami ironically plays this role when the cast visits Wammy's House.
- Lindy in the Mahou Sensei Negima! / Magical Girl Lyrical Nanoha crossover Equal And Opposite Attraction. She is often seen binging on tea and facepalming while trying to control Negi, Fate, Arf, and all the shenanigans they get into.
- Axis Powers Hetalia: Switzerland and Austria in the Alternate History 1983: Doomsday Stories make an effort in trying to be paragons of sanity in the post-apocalyptic wasteland...except that the former is doing a better job (though more of a Jerk with a Heart of Gold) while the latter is much closer to being a Broken Bird.
- Shinji Ikari in Nobody Dies, who is basically a well-adjusted and sane version of his canon self. Everyone else is totally weird.
- Even though Kyon and Chisame have had their backstories revised when they're brought into The Emiya Clan, they retain their personalities perfectly. Everyone else in the Clan is insane, weird, perverted, or otherwise, while these two struggle but usually succeed to keep their sanity amidst a household where random explosions, Eldritch Abominations, and harem antics are considered normal.
- Going by Nasuverse stats, Kyon has EX rated Common Sense. Chisame has A+.
- Andy from Calvin and Hobbes: The Series eventually became this after initially being The Generic Guy. He's usually the only one who can keep everyone in the group from arguing. Hobbes and Sherman also act like this, but have their own moments of insanity as well.
- Inspector Lestrade in the Deliver Us From Evil Series, whether among his own colleagues or Sherlock Holmes and his friends.
- In The Sweetie Chronicles: Fragments, during the prank war between the Cutie Mark Crusaders and Nightmare Moon, Twilight Sparkle takes this role.
- Naomi Misora and her son Duck in All You Need Is Love-when the paranoid neurotic and the Enfant Terrible play this role, it's saying something.
- Fluttershy and Pinkie Pie in Twillight Sparkle's awesome adventure, in two very different ways. Fluttershy is the only character whose personality isn't completely warped and who doesn't worship the metaphorical ground Admiral Awesome treads on, as well as being the one most likely to come up with good plans (which are then ignored because the author doesn't like her). Pinkie Pie, meanwhile, is a Fourth-Wall Observer in the story and therefore is the only one who realizes that the whole thing is just a terribly-written fanfic.
- In The Wizard in the Shadows this alternates between Emrys, Boromir and Aragorn, though mostly Emrys and Boromir, both of whom regard most of the cast (particularly Harry) as batshit insane.
- Anybody who knows anything about the Peggy Sue Naruto Fan Fic Yet Again knows that everyone in that fic is completely insane - except for Kurenai.
- The Reading Rainbowverse has Trixie point out how utterly crazy Ponyville is, and assume staying away assures she remains sane. Unfortunately, she has this revelation a little bit too late.
- In An Alternate Keitaro Urashima, Shinobu is the only resident of the Hinata Inn who recognizes how Granny Hina's attempts to force Keitaro to become manager aren't very nice. Later on, Haruka comes around following her Break the Haughty arc, and Urumi moves in to provide another voice of sanity.
- In Mega Man Recut, Proto Man and Elec Man are this.
- In Button Mash Isn't Dead Button Mash's Mom, Maternity is the only pony who can see and hear her (not quite) dead son.
- In the Frozen fanfic Frozen Wight, Elsa feels this way after listening to advisors who would like her to use her ice powers in ways that make money, like selling said ice directly to the public without the middleman (which Elsa refuses because that would put Kristoff and his ice harvesting crew out of business), opening more ice rinks, or creating more of the fabric she uses in her sky-blue ice dress, and other things. But Elsa gets really pissed off when her advisors suggest she create sentient snowmen to overthrow other countries.
- Bones acts as this to Kirk in most Star Trek fic.
- The Reactsverse: The eponymous characters of Weiss Reacts and Lucina Reacts are this, and Sayaka is the Only Sane Woman in Homura Reacts.
- Yu is the only Goa'uld System Lord in The (Questionable) Burdens of Leadership of a Troll Emperor who realizes they have no hope of defeating the Celestial Empire and it'd be better to make a treaty with them. Likewise, he's the only one not to engage in the civil war after Ra is killed as they're still currently at war with the Celestial Empire.
- Junko Enoshima finds herself unwittingly becoming this in The Ultimate Hope when everyone else's hope prevents them from seeing the despair in her actions (besides Mukuro, who plays along just to annoy her). And before long, after trying everything in her power to convince them of her villainy she's instead being hailed as a hero for all the hope she inadvertently created.
- In the parody fic Xtremly Scray this role is at one point filled by Voldemort.
- In the Jackie Chan Adventures fanfic The Ultimate Evil, the canon plot has an addition in the form of Valerie Payne, a young university student who's hired as the Chans' shop assistant and joins their adventures. While trying to balance her new of life of magic and danger with her university studies, she's exasperated by her extended family at times, at one point wondering if they'd turn her grey before she reaches her thirties.
- Lampshaded in Doing It Right This Time, when designated Meta Girl Asuka has a moment of slightly horrified realisation that the person to come through the end of the world and the subsequent inexplicable do-over with the least amount of mental trauma might be her.
- In No Grave Can Hold My Body Down, Chloe is the only person who thinks that maybe the goddess causing visions of death and destruction is bad news. A few cultists fear the goddess...but not enough to actually stop worshiping her.
- In Wonderful, when Taylor, Sophia and Emma are together, the latter remains level-headed and rational while their friends are busy bickering and arguing.
- A rare Only Sane Man in a group of Only Sane Men occurs in The God Squad. The Squad, made up of Princesses Celestia, Luna, and Cadence, Queen Chrysalis, Oceanic Creature Lord Tydal, and Shining Armor, tend to be the only sane ponies when they role into a town. However, when left on their own... everyone other than Shining is revealed to be nuts and Shining acts as their Only Sane Man.