Damon's old police partner, Marcus Williams qualifies as this. He's the only one to point out to Damon that his plan of he and Mindy dressing up in costumes and carrying out vigilante justice is insane.
Dave also has a moment of this, but doesn't give up being Kick-Ass though.
Mr Pink in Reservoir Dogs. He's the only one who acts like a professional. Mr Orange is an undercover cop, Mr White gets too personally involved with Orange, Joe attempts to kill Mr. Orange because of "instinct", Mr Blonde is a complete psycho, Eddie is completely ignorant of Blonde's insanity, and Mr Blue and Mr Brown hardly appear. He's also the only one to survive.
In the horror/sci-fi thriller Sunshine, Chris Evans' character Mace is the only guy who seems to have common sense and an idea of the bigger picture. Makes you wonder why he wasn't captain instead.
General Cassio Tagge at the Death Star military briefing, a pragmatist who's intelligent and self-aware enough to recognize the Rebel Alliance as the threat it is while the rest of Imperial high command is busy stroking themselves off over their might and prestige. He's a good example of how thankless a task being this type of character is; all of his very reasonable complaints are either duly ignored or met with extreme hostility, leading to the destruction of the Death Star and the beginning of the end for the Empire. In the aftermath, he manages to score a nice promotion for his foresight and intelligence... until he makes one big mistake, which the Emperor and Darth Vader use as an excuse to demote and execute him.
Leia for the Resistance, being the only competent and well-liked Commander to survive the chaotic escape at the start. Holdo keeps the ship flying onwards and never tells the crew about Crait and the rest of the crew hate her for it, leading to head-butting and mutiny when Leia is in the medbay and unable to keep everyone together.
Captain Canady for the First Order. An experienced commander who served in the original Imperial Military, he lacks the egotism and general stupidity that runs rampant in the First Order's upper echelons. In the opening battle, he's the only commanding officer who recognizes the Resistance's obvious strategy (he even has to explain to his clueless lieutenant that the puny fighters shooting at them are trying to take out their anti-air cannons, not blow up the ship). His sanity almost manages to salvage a fight that General Hux screwed up from the get-go, but the incompetence of his bridge crew ruins it; Canady spends his final moments screaming at them to stop screwing around and shoot down the huge bomber that's about to kill them all. They don't.
Ironic in that it was Chapman who frequently played the zaniest Cloudcuckoolanders in the series.
Chapman has also been cited as the funniest of the Pythons by the others, although hampered by alcoholism. He was certainly the edgiest: his writing contributions to the series are easily discernible by their being markedly more unpleasant, mean-spirited and of general poorer taste then the others (a notorious example being the undertaker sketch where Chapman's undertaker is suggesting they eat the corpse of Terry Jones' dead mother, "and if you feel guilty later we can dig a grave and you can throw up in it"). One theory as to why series 4 was so much nastier than the first three is that John Cleese - Chapman's traditional writing partner and moderating influence — had left the group.
In the Death sketch in Monty Python's The Meaning of Life, the Grim Reaper gets this role. He comes in to claim the souls of a bunch of people in a dinner party but it takes five minutes for them to understand that he's not there to reap the hedge, doesn't want wine and won't discuss philosophical topics with them.
Robert: He knows the song too? I've never heard this song before! What the hell is it?!
Arsenic and Old Lace (1944), with Cary Grant as Mortimer Brewster, the token Only Sane Man surrounded by his rather... quirky family. Insanity can be contagious, if only because we as humans derive our idea what is sane from the people around us.
Unusual in that it is one of the very few examples in which the rest of the characters are, in fact, completely mad, and not just irrational, carried away, or mind controlled.
In Jurassic World, Owen Grady is this at several points. He thinks creating any type of super-hybrid is a really bad idea and stares at Hoskins like he's insane when the other man suggests using Velociraptors as field weapons. When the I. rex escapes, he immediately suggests evacuating the island and using every BFG they have against it.
Claire: Corporate felt genetic modification would up the wow factor. Owen: They're dinosaurs. Wow enough.
Nicholas Angel in Hot Fuzz, surrounded by a lazy police force who don't take any of his suspicions seriously.
"Am I going completely mad?!!" [silence]
Francis, in The Cabinet of Dr. Caligari, is the only person who realizes that the incredibly sketchy Dr. Caligari and his Brainwashed and Crazy servant Cesare are murderous psychopaths. Subverted when Francis is revealed to be insane and the whole movie was the babbling of a Talkative Loon. It turns out that Dr. Caligari is the only sane man, except his name isn't actually Caligari. At least, if you consider the bookends to be canon — many do not, given that they weren't part of the artist's original vision, but were added via executive meddling. The suits thought that the films central message of "sleepwalking obedience to authority can result in Bad Things happening" was too reactionary and controversial, and insisted on the bookend scenes to tone it down/subvert it. The movie was made 1930's Germany — how could unquestioning obedience possibly lead to anything bad?
Shaun of the Dead: Nobody, with the possible exception of Yvonne, begins as this—they can't even comprehend the idea that the dead are rising up and trying to eat them, and fall back on pretending there's nothing wrong. However, Shaun evolves into this when he finally decides to fight back. Of course, 'sane' is relative as his plan to hide in a pub gets most of them killed (the other survivors we see flee in the opposite direction and do much better).
In I, Robot, when Doctor Calvin calls Detective Spooner insane after he shoots a (blank and mindless) robot in the face, he replies "Does thinking you're the last sane man in the world make you crazy? Because if it does, then maybe I am."
An incredibly depressing one in HBO's Conspiracy (2001), which is a dramatization of the real life Wannsee Conference where the details of the Final Solution are worked out and the various relevant individuals notified, comes in the form of Dr. Kritzinger. He tries to make a moral stand while everyone else is concerned with bureaucracy or power-play, but he's shot down and eventually goes along with it after realizing the futility of objecting. It is summed up by this exchange at the end of the film:
Kritzinger: It is night in Moscow already. Soon it will be dark here. Do you think any of us will live to see the daytime? General Hoffmann: Come spring we will be on the move again. Keep your spirits up.
Mr. Furious: That's because Lance Hunt is Captain Amazing. Blue Raja: Oh, here we go. Shoveler: Oh, don't start that again! Lance Hunt wears glasses. Captain Amazing doesn't wear glasses. Mr. Furious: [Long-suffering] He takes them off when he transforms. Shoveler: That doesn't make any sense. He wouldn't be able to see!
Part of Mugatu's Motive Rant / Villainous Breakdown in Zoolander is his claim that all of Derek's looks are identical. (See the quote on the works page.) This is enough to spur Derek into creating a new look that involves turning left instead of turning right, which has the power to stop a shuriken in mid-air and even Mugatu thinks that it's beautiful.
Even then, the new look is a mirror reflection of all his others.
Subverted by Truman in The Truman Show as he slowly figures out that he is living in an artificial world; of course, the other actors are already aware of it, so they try to disabuse him of the notion when he explains his concerns to those around him.
Buck in Uncle Buck, especially during the second half.
Agatha in The Grand Budapest Hotel points out some of the more absurd elements of the film that every other character takes completely seriously.
A famous example is Zeppo Marx from the Marx Brothers films. In a group of comedians with defined by distinct comedic styles (The comedy of Groucho, Harpo and Chico came from wit, slapstick and double-entendres, respectively), Zeppo was defined only by his lack of a "quirk". His roles were the definition of a straight man. Margaret Beaumont's characters also tended to fill this role, mostly serving as someone for Groucho to talk to.
The Bridge on the River Kwai ends with Major Clipton looking around at the carnage and destruction surrounding him, and declaring, "Madness! Madness!"
Kevin Sandusky and to a lesser extent Alpa Chino spend much of the film trying to rein in their unhinged costars. Their success is limited.
Kevin Sandusky: Tugg. Tugger. You're the last piece of the puzzle buddy. We need you! Your men need you. Are you with us? Tugg Speedman:[pause] I'm a rooster illusion. Kevin Sandusky: Fuck it. We'll deal with him later.
Kirk Lazarus has flashes of sanity, usually to contrast with Tugg. As a general rule within the film though, the sanest person in any room will be the one with the lowest status. (For instance, Kevin is most sane because he's the least famous actor.)
Laurie and her school newspaper staff in The Wave, among the few students who are trying to stand up to the quasi-fascism sweeping their school.
Jaws: Matt Hooper tells Chief Brody that he will be "the only rational man left on [Amity] island" after Hooper leaves the next day to join a shark research vessel.
Ted in Burn After Reading. A former man of the cloth, he now works at the Hardbodies gym. He is practically the only normal character in the entire film, which is filled with delusional characters who are mostly Too Dumb to Live. Ted nurses an unrequited crush on his colleague Linda, and she is blissfully oblivious to his quiet affection. At the end of the film, it's revealed that Ted was shot and killed. With a hatchet.
The CIA director as well.
In Dagon the only sane man is the town drunk. Uh-oh...
Played with in What About Bob? At first Dr. Marvin is the only one who sees anything wrong with Bob's obsessive, manipulative, stalker-ish behavior. Bob becomes better socialized and more acceptably-quirky over time. Dr. Marvin tries to kill him as revenge for earning his family's appreciation.
Duncan, sort of, in Mystery Team. Although still maintaining his childish personality, he is slowly revealed to be more and more normal than we are led to believe.
Chef in Apocalypse Now was described by Captain Willard as being "wrapped too tight for Vietnam; probably wrapped too tight for New Orleans."
Smith in Sleeping Dogs attempts to stay aloof as civil war breaks out, but is caught up with it despite his best efforts. He spends the rest of the film vainly trying to escape the madness, without success, until the end where he seems to bitterly accept his fate at which point he gets killed.
Peggy in The Woman is the only one who really criticizes her father Chris's idea of trying to "civilize" the feral woman he captured, what with her mom Belle being too henpecked to stand up to him, her brother Brian being too much like his dad, and her little sister Darlin' being too young and naive to know any better. She's also the only member of the family, other than Darlin' and their feral sister Socket, to survive to the end.
Alan is this in American Dreamer, due to "Rebecca's" antics even getting the police to believe her over him.
Agent Coulson in The Avengers. Fury is busy trying to control and lead the Avengers around by their noses, Steve is blindly obedient to Fury for the first half of the movie and wrapped up in fighting with Tony and Thor, Natasha is openly disdainful of and uncommunicative with the rest of the group, Thor is preoccupied with Loki and being a Fish out of Water, Tony is flippant, abrasive, and always at SHIELD's throat, Bruce is paranoid and suspicious of everyone, Clint is a brainwashed minion, and everyone is constantly bickering. In the end, Coulson is the only one who has it together enough to think ahead and head off Loki's escape attempt with a special BFG cannibalized from Asgardian tech, and understand that the Avengers need something in common to fight for before they can be of use. His subsequent murder, which was partly the Avengers' fault (as they were too busy arguing to catch the ambush Loki's minions launched on the Helicarrier before it happened), causes everyone to go into Let's Get Dangerous! mode pretty quickly, and Steve takes over the Only Sane Man position.
Corporal Joe Bowers in the 2006 Mike Judge cult comedy Idiocracy, who having been stuck in suspended animation for over 500 years while humankind has grown progressively stupider and stupider, awakens as unquestionably the smartest man in the world. Alas, Joe's notably superior intelligence is often for vain when dealing with the dunces in this idiotic dystopia, which is played for laughs throughout various situations at Joe's expense. At one point, Joe asks members of the President's cabinet why plants are being watered with a Gatorade-type sports drink, Brawndo; their only response is to repeat Brawndo's advertising slogans over and over to him ad nauseam. Even when compared to his only other current-day contemporary, Rita (a former prostitute), Joe comes off as clearly more sensible (given that Rita is convinced her former pimp could travel through time to find her.)
The first mate in Ghost Ship. After Santos is killed and they're stranded on the Graza, Greer is the only one to really show concern that the ship might be haunted, and that they should forget the gold, forget salvaging the ship, and get off immediately. However, Greer himself is subsequently lured to his death by Francesca. He didn't fall for greed or wrath, so they got him with lust instead.
Ed Du Bois is probably the only logical and sane character in Pain and Gain. All others do stupid errors, none moreso than our protagonists.
In King of Hearts (1966) Private Charles Plumpick is literally the only sane man in the French town of Marville, due to it having been evacuated by the regular citizenry before being repopulated by escaped denizens of the local insane asylum.
Pete from Neighbors is the sole member of Delta Psi who actually has plans for life after college.
In Teenage Mutant Ninja Turtles (2014), Leonardo's the first one to put his foot down when his brothers get too distracted, making sure they focus on what's important at the moment.
Greedy: Robin is the only one in the film who desires to walk away from the fortune when he sees how unscrupulous Danny has become, and warns him to just walk away.
Ed is just as greedy as his cousins, but he understands the damage competing for an old man's fortune has done to him and everyone else, and is able to find the words that makes the whole family almost walk away.
Hogan in The Scribbler is a literal case. To take advantage of being the only guy in a psychiatric halfway house occupied by many women starved for sex, he happily feigns being mentally unstable; at one point, he considers faking multiple-personality disorder, asking his friend Suki (a legit Split Personality sufferer) for tips.
A Very Brady Sequel: Trevor is a thief impersonating Carol's long dead husband to steal a priceless artifact, but he is more rational than any other character in the movie.
Merlin in Kingsman: The Secret Service. Especially after Harry's death. And upon finding out Arthur had compromised the Kingsmen by siding with Valentine, he's the only one trusted by Eggsy and the new Lancelot to help them stop the Hate Plague.
Running Buffalo, along with the rest of the Comanche, in McLintock!. They're standing around most of the movie watching crazy white folk act up.
Over the Edge: Julia, the community center supervisor, is the only adult in town who really sympathizes with the kids of New Grenada and tries to listen to their needs. Carl is this among his friends, trying to avoid engaging in delinquent behavior, until he gets fed up with his parents' behavior and runs away.
Peter is the only one who appears to have a clue that, for example, playing football in tuxedos is a bad idea or that Lisa has some serious Lack of Empathy issues. He disappears halfway through the movie, since the actor had other commitments, with the unintentionally hilarious line, "That's it. I'm done."
Downfall: Albert Speer is one of the few people who realizes the war is lost and refuses to carry out Hitler's order, and forgoes suicide, believing Germany can still have a future.
Roslyn in The Misfits is the only character in the film with any common sense, while the men around her are either reckless fools or selfish jerks who want her for her body.
The Woman in Red: At what turns out to be Teddy's birthday party, where Charlotte discovers Teddy had been lying to her, his friends make the save by telling him about Joey breaking down since Teddy is "the voice of reason."
Help!: Ahme is the only person with any lick of competence in the movie, and she seems rather exhausted by it.
Walter Greenbaum, Max's attorney in What's the Worst That Could Happen?. He spends the entirety of the movie attempting extract Max from holes that he insists on digging for himself. He repeatedly tells Max to give the ring back, as the longer he keeps it, the more money it winds up costing them. When Max refuses and insists on going down the path he is on, Walter quits, gets out of the car and walks away, never to be seen again
Joanna in Office Space is the only character who doesn't have a character flaw, annoying trait, or who conducts morally questionable acts.
In Mortal Engines, when MEDUSA is revealed, Historian Pomeroy is the only one to react with horror while the rest of the citizens celebrate raucously.
Todd in Dead Birds. While he initially shares this with William who acts as somewhat of a Reasonable Authority Figure at first and possibly Sam, he is the least susceptible to blind materialism once he realizes why they were brought to the house in the first place.
6 Underground: Seven, who objects to a lot of One's orders and protocols as being unnecessary and dangerous. Justified as Seven's former Delta Force, whereas the rest of the team, excepting Two who's CIA, are civilians or criminals.