The "Chicken Boo" sketches on Animaniacs had only one person realizing that Chicken Boo was actually a giant chicken in a ludicrously flimsy disguise. Nobody would believe them (or misinterpreted the use of 'chicken' as an insult, as in coward), and even when Boo's deception was eventually revealed (by some event unrelated to their efforts), they never got any credit for their insight.
Animaniacs also had Dr. Scratchensniff, who's powerless to either stop or tolerate the zaniness personified that is the Warner siblings.
Happy Time Harry in "The Last One", as he was the only one who noticed the Aqua Teens were in Carl's house.
Carl is a downplayed example. He's an unhygienic, sex-crazed, misogynistic, lazy bum; on any other show, he'd be the wacky next-door neighbor, however considering that he lives next door to a trio of sentient fast food items, he's the sane one by default, in addition to being the token human.
Even more so Suki, when she is with the group. She's the only of the main and recurring characters who could be considered to be normal. She takes it quite gracefully, though.
Also Katara sometimes, most notably in the episode The Runaway, in which she is the only one who realizes that excessive scamming of scammers will come back to bite them eventually. Toph started the whole thing, and Sokka being involved is not horribly surprising, but Aang should have known better.
In Sequel SeriesThe Legend of Korra, Tenzin is this to the council as a whole. They don't seem to realize their decisions and actions are further proving the point the Big Bad is making, and he is even outright ignored. To further it, he also plays the role to Korra and (in a comedic sense) to his family.
Mako (and to an extent President Raiko) is becoming this in the second season. Midway through, he's the only one interested in figuring out who's behind a string of bombings in Republic City beyond making the presumption that it's all Northern Water Tribe, as everyone else is acting according to Varrick's manipulations. Korra's hell bent on getting revenge against the North for both Unalaq's machinations and the above misattributed offenses, Bolin's become wrapped up in new celebrity status, Asami's struggling to keep her company afloat and losing hope because of it, and even Lin Beifong is pulling rank on Mako in favor of two mustache-twirling detectives who don't seem to be doing their jobs. And of course Varrick is pulling everyone's strings in the name of War for Fun and Profit.
Between Eska being an abusive psycho and Unalaq shaping up to be some sort of Well-Intentioned Extremist regarding the Water Tribe's spiritual issues, Desna's developing habit of asking questions is putting him on the road to this trope within his family.
In Book 4, Tenzin's kids Jinora, Ikki, and Meelo are sent to find Korra. Despite the fact that Jinora is both extremely knowledgeable andthe youngest master airbender, Meelo is the more natural warrior, it is Ikki who takes on this role. Jinora is self absorbed with her spiritual powers and so doesn't bother investigating through any other means, even when her powers don't give her any leads. Meelo wants to turn this into a grand adventure, throwing away the food and declaring that he will hunt(until Ikki points out that they are vegetarians). He then goes foraging and only finds some bad berries that make him and his lemur ill. Ikki meanwhile manages to actually find Korra's general location. Even though she is captured, she still manages to get more information out of her captors than they get out of her before talking her way into being released. Jinora and Meelo's "rescue" turns out to be pointless.
Bob of Bob's Burgers is (usually) the most mature and sensible member of the Belcher family, objecting to whatever craziness Linda and the kids have planned.
Captain Star's First Officer Scarlett is the one who actually gets the work done between an egotistical captain, a fish obsessed cook and an engineer whose isn't that crazy, in fact, he's perfectly sane. He has nine sane heads on a single body.
In CatDog, Mervis and Dunglap are more or less the only normal characters in the series.
Shnitzel from Chowder is usually a good example, though he does a have a few lapses into the weird goings-on in the show.
Number 1: Abby, we both know you're the only one on this team with any real common sense. When I'm screaming that we're being invaded by tiny, kid-eating leeches falling from the sky, you're the one telling me it's only snowing.
Elise is probably a better example, given Chris tends to go along with Dan's schemes. Though she does have her moments of Not So Above It All.
Danger Mouse. He has to deal with a Cowardly Sidekick (Penfold) and an addled, near-senile superior (Colonel K). DM will either take the initiative and stop their banter or just throw up his arms in defeat.
Daria can basically be summed as two of these characters (Daria herself, and her best friend Jane) trying to endure a satirical version of a 1990sHigh SchoolDramedy. Other characters, particularly Jodie and Tom, can also exemplify this trope on occasion.
Lee, the protagonist of Detentionaire, is this on his show. When he's not available, Tina tends to step into the role.
Although only sane person is stretching it, Foxxy Love on Drawn Together was once accurately described as "The only one here who's not completely retarded." Spanky Ham also fits this role after getting over his Early Installment Weirdness; he's often one to give a speech with the reasonable solution to an issue, like saying that old cartoons with racist stereotypes may be offensive, but denying them as part of our culture is dangerous.
Edd (also known as Double D) is usually much more reasonable and mature than his friends. This is probably the reason why the Kids like him the most out of all 3 of the Eds.
Nazz is generally the most mature of the cul-de-sac kids, although she later becomes something of a ditz.
Major Doctor Ghastly from Evil Con Carne fits the role because she doesn't like it when things get out of hand for her lover reduced to a brain.
On The Fairly OddParents!, Wanda is usually the only one aware of how insane everything is, or knowing of how bad everything is going to end up. This fact is often pointed out by Timmy and Cosmo, but they still continue with their antics despite that.
During the first season, and whenever fairy culture, rituals and quirks are involved, Timmy often assumes the role of the only sane man. As an outsider, he seems to be the only one to notice how weird that world really is.
Family Guy: Brian Griffin is often portrayed as the Only Sane Man, although everyone who isn't Peter ends up playing the Only Sane Man once or twice.
Hermes often takes this role most notably in Bender's Big Score where he's the only person to realize the crew is being scammed. He's also the most consistent critic of the incompetent Zoidberg.
Hermes' role is well exemplified in "The Duh-Vinci Code":
Professor Farnsworth: We must fly to Rome and exhume the body of Saint James! To the ship!
Hermes: Didn't we used to be a delivery company?
Professor Farnsworth: TO THE SHIP!
Leela is easily the most level-headed person, compared to Fry, Bender and the others. Though she has her moments, particularly when she is insulted. She holds very strong grudges.
Goof Troop has Peg and PJ both in this role; however, usually not at the same time, as Peg tends to have little screentime in PJ and Max episodes and PJ acts as a Satellite Character in most Pete and Peg episodes. Overall, Peg is more likely to be silly than PJ is, and PJ is more likely to misunderstand a situation than Peg is—despite this, both are usually the voice of reason for the others. Also, the characters are far more likely to listen to Peg than they are to PJ because Peg is far more assertive than her son is. Considering the rest of the cast consists of a Cloud Cuckoolander, an irrational Jerkass, a Fearless Fool, and a Genki Girl...
Dipper Pines from Gravity Falls is one of the few people in the titular town to actually acknowledge the supernatural occurrences and the citizen's wacky antics.
Lin Chung of Hero: 108 is always calmer than the rest of the cast.
The Hollow: Skeet's the only one on his team who is concerned about the growing glitches in the world and was even willing to hear the other team out before his own team overrules him.
In Happiness Is a Warm Blanket, Charlie Brown, Linus calls everyone out for trying to break him of his security blanket habit by pointing out all their eccentricities and challenging them to identify the one person among them who is truly secure. It's Pig-Pen.
In Invader Zim, Dib and Gaz are both in this role, as they only ones who know that Zim is an alien, no matter how blatant it becomes. Gaz arguably even moreso, as while Dib obsesses over Zim's constant plots, Gaz is all too aware that Zim will screw himself over with or without Dib's intervention.
Originally, both of the Tallests were shown to be somewhat moronic, but Red's Divergent Character Evolution was sending him in this direction, best evidenced in "Backseat Drivers from Beyond the Stars".
Kim Possible has Shego. Any episode featuring Doctor Drakken will have her standing off to the side making running commentary on the absurdity of his plan, or how it will inevitably fail because of one major overlooked factor. It is also implied in the episode 'Go Team Go' that this was the reason for her leaving the team of superhero siblings and going bad.
Hank Hill of King of the Hill is a shining example. In his version of the Rashomon, he sees himself as the only adult among children, and in a hallucination caused by varnish fumes, he imagines the rest of the world as helpless rodents on a Whack-a-Mole board.
Boomhauer also plays this role too. While he certainly does pick up the Idiot Ball on several occasions, he's easily the most rational of Hank's friends. Heck, Hank barely has to babysit him at all, he even complained once about not being in hot water with Boomhauer since it would be less taxing than Bill and Dale.
Possibly Justifiable in Boomhauer's case in the episode "A-Firefighting We Will Go", Boomhauer's recap of the events show Hank, Bill and Dale talking in Boomhauer's signature speech pattern, and Boomhauer talking like a normal person without his signature fast-paced and somewhat incoherent speech pattern.
Dale: Yeah, man, I tell you what, that dang ol' detector, man, talk 'bout government take away freedom of smoke, man. Talkin' 'bout yo, man. Hank: Yeah, man, I tell you what, man, dang ol' boy ain't right, man, talkin' 'bout kicking 'dem dang 'ol ass, man. Boomhauer: For God's sakes, Hank, act like an adult, man. And keep it down, guys, will you? I am trying to get through an article on vintage Camaros, and I've been on the same dang page for twenty minutes. Bill: Dang ol' pretty pretty pizza, man, I tell you what.
Les Sisters: Sammie. She spends most of her time hanging out with Wendy, who tends to overreact to things and come up with stupid ideas to get things she wants, Marine, who is Wendy's annoying little sister, and Maxence, a rare male example of a Dumb Blonde.
Bugs Bunny, of all people, spends time in this role in episodes of The Looney Tunes Show. Mind you, when you spend most of your time with a) Daffy and b) Lola, it's hard to avoid this characterisation.
Charles Offdensen from Metalocalypse. We actually see him go through the three stages in the background; by the time season two ends, he's learned to roll with it. Season three sees him realize that he's not the Only Sane Man. He's just the Only Sane Man on his side of the conflict.
Tommy Anybody from Mr. Bogus invariably falls into this role, when having to deal with the wacky antics of Bogus (and occasionally Brattus).
Adam Lyon from My Gym Partner's a Monkey - being the token human in a school full of animals (anthropomorphic ones at that, but still stupid, jerkish ones) - is the sane one by default, and serves as the voice of reason for his entire school.
Of the Mane Six, Twilight Sparkle usually plays this role, often being bewildered by her friends' antics, and patiently offering impartial observations and sound advice (that is only sometimes followed). But that doesn't make her immune to occasionally being tossed the Idiot Ball or suffering Sanity Slippage; at which point, Spike or Applejack will take the role. That said, circumstances occasionally allow any of the Mane Six (even Pinkie Pie) to hold this position.
Of the Cutie Mark Crusaders, Sweetie Belle is often quick to criticize the more dangerous and ridiculous plans the group comes up with, and also suggests to "tell an adult" as a course of action when a problem gets too difficult for the CMC to solve.
Of the pets, Owlowiscious is easily the smartest and sanest. In "Just for Sidekicks" he's the one who helps Spike keep the other pets in line, and in "Inspiration Manifestation" he tries, in vain, to warn him against using the Tome of Eldritch Lore.
Ned's Newt: Ned often acts like this, being bewildered at how crazy the people around him seem sometimes.
Private is the most down-to-earth and rational of The Penguins of Madagascar despite his naive, nice guy attitude. Generally speaking, it's him, Maurice, Marlene (except when she's outside the zoo grounds or talking about Spanish guitars), and maybe the chimps who are the most reasonable of the cast.
The Sanity Ball can be passed around, however. Rico once, actually. In "The Hidden" he keeps Kowalski and Skipper focused on the task at hand (finding their friends). Skipper, in any episode where the penguins encounter anything that terrifies them like in Snakehaed! or in any situation where he dope slaps all three of them at once. Kowalski, almost never. Though he thinks he is. Julien, no way. Mort, uhh... No...
Several characters from Phineas and Ferb fall into this trope, but, at some point, most characters get swept up in the show's general inanity. Despite being, well, a platypus, Perry plays the straight man to Doofenshmirtz.
Stacy fits this trope when paired up with Candace.
While Jeremy is in on the show's zaniness, there have been times when one can see the Flat "What" expression on his face. Case in point:
Many of Townsville's inhabitants usually have very little common sense or are mean-spirited and malicious. In the midst of it all is Miss Bellum, who is much more competent and intelligent than most of them, including the childish and dim-witted Mayor.
Professor Utonium also qualifies for similar reasons. He's not only a very good and capable father towards the girls, but he actually has enough level-headedness to come up with a practical solution to something.
In Ready Jet Go!, Sean and/or Sydney usually have this role. Sean has this role when the other kids are jumping to logically impossible conclusions and deliberately making mistakes, and Sydney is this when the kids are making dumb decisions and Sean is being Out of Character.
Karl Pilkington of The Ricky Gervais Show. While Ricky and Steven laugh about all his thoughts, a fair number of his questions and statements are perfectly logical: notably a thought experiment where he wondered if one would be able to confidently state that they are the original if they had a clone with all the same exact memories up to the point of their creation.
YAY-OK from Rocket Monkeys typically falls into this area, as he's the only halfway competent or intelligent member of the crew. He doesn't seem terribly frustrated by Gus and Wally's stupidity, though.
Rocko from Rocko's Modern Life seemed to start out this way, a hapless bystander trying to use logic to navigate a thoroughly insane environment and oftentimes failing. Strangely, he seemed to lose this as the series also took a turn away from being as surreal as it once was.
In Sealab 2021, Doctor Quentin Q. Quinn is the Only Sane Man. At least in the beginning of each episode. Often the sheer insanity of everyone else becomes contagious or he would get fed up with the insanity and blow up Sealab.
She-Ra and the Princesses of Power: This could be Bow's job description. If he wasn't the friendliest man alive, he'd probably go nuts trying to ensure some degree of sanity prevails despite the eccentricities of Adora and Glimmer. Most obvious in "The Beacon", where he's the only one who points out that blindly trusting that Adora is going to figure out how to use her sword to heal at this exact moment is probably not a good plan.
The episode "Homer's Enemy" featured the character Frank Grimes, who is the only one of Homer's co-workers who recognizes his pathological boobery. He tries to point it out to everyone, but to no avail. He eventually works himself up over it so much that he has a nervous breakdown, during which he accidentally electrocutes himself. After some fans complained his treatment seemed a little mean-spirited, DVD commentary explained Frank was mainly a device to show a normal person couldn't function in the show's universe.
Lisa Simpson also often finds herself thrust into the role of only sane...girl. Quite often, when her family (or occasionally, the entire town) is caught up in some insane course of action, she's the one who points out how absurd things have become. Her comments are usually ignored. The straight man role is usually traded between Lisa and Marge. Sometimes Lisa is also caught up in the craziness, for example with the Movementarians.
There are even times that only the Simpson family really know what's wrong, and have the guts to do something about it, putting the whole family in this role.
Lou is the only sane man in the police force in Springfield, and frequently points out Chief Wiggum's incompetence or stupidity.
Carl Carlson is this, at least in comparison with his friends.
Other characters to have this role on a semi-regular basis include the more conventionally competent characters such as Apu (and his brother Sanjay is this to him when he has gone a bit too far with his work), Dr. Hibbert, Superintendent Chalmers, Sarah Wiggum (within the Wiggum family - "Clancy, use the remote") and Waylon Smithers.
Word of God states that Chalmers and Grimes were written as the only people who could function outside of Springfield. Chalmers just takes a different track from it to Grimes, choosing to not be botheredby all the insanity around him. This is perhaps most famously shown in the "steamed hams" scene, where Chalmers accepts Skinner's Blatant Lies at face value: he knows that Skinner is lying, but he's pretty sure actually pressing those lies would just lead to him getting wrapped up in something stupid.
Panda of Skunk Fu! knows what's best for Skunk (seeing that he's his master).
Louise in Slacker Cats is the voice of reason throughout the show but Buckley does zig-zag between being this and one of the many crazy people/cats throughout the show.
Stan. Kyle has the appearance of being sane as well, but unlike Stan, is unable to understand just how moronic the actions of all the insane people around are. Among the adults is/was Chef and, on occasion, Jesus.
Wendy is definitely this amongst the girls (and more often among the entire school).
In the "Pandemic" episodes, Craig took on this role, as he spends the episode calling out the main boys as being jerks that constantly get themselves and others into ridiculous situations, entirely in deadpan delivery.
Craig: "You guys took my birthday money, got me arrested and sent to Miami with no way home except to take down the country of Peru, and I'm being a dick?"
Cartman: "There's no talking to this guy."
Kyle's tendency to have quite a temper to the extent of being damn near bipolar excludes him from this on a regular basis, but there are instances where he plays this straight. The episode concerning the economy and the absurdity of aestheticism is a crowning example. Even "You're Getting Old" has him playing this to Stan of all people.
When he was around, Chef was usually one of the very few adults with any kind of common sense.
Sharon has become the closest to fulfilling this in Chef's absence.
President Bush, ironically enough, especially when compared to his cabinet and the press. "A Ladder to Heaven" contains a particularly infamous example.
By this point, it appears that Kenny is the only one that has showcased routine common sense throughout the series. This is arguably lampshaded by Butters (of all people) in "Going Native" where, after chewing out most of the others kids for their quirks, claims that Kenny is the only one with "any sense of dignity."
Apparently, Father Maxi is the only catholic priest who doesn't rape boys.
Mr. Garrison (and to a lesser extent Clyde) in Lice Capades.
Robert Johnson, Andy's father, seems to be the one of the very few people on this show with any rationality.
Andy himself is a rare child example, for he's usually the voice of reason to his idiotic pet/best friend Rodney. However, on very often occasions, he suffers from Ping-Pong Naïveté and as such can go from this to holding the Idiot Ball very quickly, with such examples being the episodes "The Big Haggle Hassle", "Endangered Species Twist", "Harried Treasure", and "Freaky Furday".
Sludgy Dave from the episode "Ice Cream Anti-Social" is actually helpful to the younger characters and strives to solve his customers' problems. He's also one of the few examples of this trope who isn't a Deadpan Snarker or a Butt-Monkey.
The titular character of Steven Universe must occasionally play this role when things get too emotional among the Crystal Gems. This gets lampshaded in the season four episode "The New Crystal Gems", where his best friend Connie is pushed into the role during his absence and remarks in a short "The Reason You Suck" Speech how ridiculous it is that a child like her is more emotionally mature than aliens that are thousands of years old.
His mother, Pink Diamond, also plays this part to the other Diamonds, being the only one of them who sees the value in organic life and treating her Pearl as an equal.
Titan Maximum deconstructs the idea of the Only Sane Man with Gibbs. Being the only competent member of the former Titan Maximum team eventually drove him into hating everyone else on the team and performing a FaceHeel Turn on the first episode. The fact that he's the Only Sane Man makes him a very effective villain, albeit an incredible Smug Snake.
Gwen from Total Drama is one of the most normal contestants, and qualifies as this for most of Total Drama Island.
Noah is more of a classic example, especially when you compare the rest of his team in World Tour (excluding Alejandro, who gets this whenever Noah's having fun).
Transformers: Prime actually has this in one of its human characters, Jack Darby. Unlike almost every other human in the Transformers universe, he knows that getting yourself involved in the front lines of an alien robot war is more dangerous than awesome. In fact, he tried to avoid all contact with the Autobots at first before some convincing.
The villains have Soundwave, who doesn't share the sociopathy or megalomania of most of the other Decepticons and is far and away Megatron's most loyal and competent henchman. Be warned: This trope does not in any way make him less dangerous than the others. At all.
While Kitty from T.U.F.F. Puppy has the occasional tendency to act as goofy as everyone else, she is the most level-headed character when compared to Dudley, or anyone else on the show for that matter.
Bob the Tomato, in the VeggieTales cartoons — in the opening and closing sequences where he plays himself, he consistently provides a voice of reason on the show. During the actual episodes, he is almost invariably cast in the role of a character who is competent and sensible, unlike most of the others.
The Venture Bros. has Doctor Venture, who often tries to be the Only Sane Man, but the intense neuorses and truama of being a boy adventurer keep him from suceeding, resulting in a very broken man. Usually, the role ends up being filled by one-shot bad guys that question the Venture Team's logic. You know you have problems when a flamboyant super-villain is judging you.
Brock fills this role quite often as well, in spite of murdering multiple people on an almost daily basis. He's generally the sanest, most level-headed and most competent member of Team Venture, so it's not hard for him to slide into the role and see just how absurd his life and the lives of those around him are.
Dr. Venture:(As a party being thrown by his brother sits on the brink of collapsing into madness) Huh. When you're not the one in the middle of it all, it's actually pretty obvious.
Brock: Welcome to my world.
On the villains' side, Dr. Girlfriend is likely the closest thing to a competent one (at least compared to the Monarch and anyone else affiliated with him).
Dean Venture may also be growing into this role, as he's developed some sense of what normality is like and would rather like to give it a shot. This does contrast against his brother Hank who loves the life (and does help Dean accept it all with a more positive attitude). Whether Dean will succeed is another thing, since it's implied Rusty tried to be normal, but gave up on it a long time ago (it's implied one reason for his bitterness is that while the world has forgotten him for the most part, he still has to deal with supervillains.)
On the Animated Adaptation of Wayside, Todd is repainted as the only one using real world logic while everyone else is using bizarre logic of the school.
In the X-Men animated series, the largest of the sentinels (robots designed to capture people) is called Master Mold. He/It starts trying to take over the world. When reminded by his creator that his mission was to protect humans from mutants, Master Mold says, "That is not logical. Mutants are humans. Therefore, humans must be protected from themselves." Not a bad realization for a robot antagonist that Professor X called "the embodiment of human hatred" that was created by another antagonist.