24: This trope also reveals itself very early on with David Palmer's wife, Sherry...aka the eventual First Lady. At first she appears to be a generic, stereotypical "politician's wife", dressed in pink, dowdy outfits and pearls and posing for awkward photo ops. Then over the course of the day it's hinted that beneath this façade she's quite savvy at political hardball herself and is willing to step on a few toes to help her husband win. OK, nothing too bad just yet. But then it gradually becomes clear that she's been involved in some very unsavory dealings in the past and that she still is. And once her husband discovers this (even he didn't know just how bare-knuckled she actually was), she drops all pretenses (at least in front of him) and basically reveals herself to be a cold, cynical and downright nasty Lady Macbeth-type figure. And she's freaking scary. At one point, she even tries to convince an intern to sleep with her husband because she's hoping to use her to spy on him. It gets especially creepy when we see her doing these unsavory things and spouting borderline psychotic dialogue while dolled up in the most cutesy, matron-like outfits ever, further underlining just how much of a Unstable Smiler she really is. Also, anyone who finds out about her true personality — including her husband the President — becomes utterly terrified of her. At one point she actually kills a guy by TALKING TO HIM.
In Agents of S.H.I.E.L.D., Simmons becomes this in early Season 2 while working undercover in a HYDRA lab. She's constantly bright, cheerful and full of smiles for her co-workers, but is secretly terrified of being discovered, not to mention having to hide her revulsion for them since they're working for HYDRA. It goes a step further when asked by Coulson how she's feeling being undercover, as Simmons claims to be fine, but Coulson is quick to deduce that she's barely eating and feels isolated.
Alex Rider: Alex and James are deeply disturbed when their friend Laura suddenly joins the "good" pupils, literally overnight. Later, the same thing happens to James. They're being replaced by clones of Dr Greif, surgically altered to look like them.
Bernadette on The Big Bang Theory is solidly Unstable. She always wears the same smile, even when saying some incredibly creepy and threatening things (such as crossing Ebola with the common cold, or advising Howard on how to talk to her father).
The Bones episode "The Death of the Queen Bee", set at Bones' high school reunion, references this trope, specifically Unstability. A janitor who looks extremely suspicious (played by Robert Englund, even!) is completely benign, while the actual murderer turns out to be a Stepford Smiler. To quote the janitor: "One look at her, you can tell she's off. Them smiley ones, they always give me the willies."
Charité at War: Otto acts as a carefree, charming, sunny young man when he returns from the World War II front. He's actually miserable, plagued by nightmares, and neither his sister Anni nor co-veteran Martin are fooled.
Martin: You can't sleep without light either, huh?
Shirley displays a mild side of the trope, but she is known to have "thinly veiled rage issues" under her cheer.
Annie has moments of this as well, especially in the episode where she's planning to start a Model UN, and Other Annie steals her idea, prompting a Model UN-off to decide whose Model UN will be the official one. Annie spends the majority of the episode smiling and laughing in an unconvincing manner while clearly on the verge of a nervous breakdown.
Annie: Everyone should just have fun. But then again, what's more fun than winning? (laughs hysterically)
Daisy from Dead Like Me. She starts out as a ditzyHard-Drinking Party Girl and former actress who Really Gets Around, loves to brag about it, and acts more than happy with herself, but then her last thought is revealed: "Why has no one ever loved me?", revealing that she only acts happy with her life (and her un-life, given what the show is about). Although the Alpha Bitch and Narcissist things she also does, when viewed in conjunction with the smiling, give you sort of a clue from the beginning that something is wrong.
Bree stands out as the most Stepfordish. In the pilot, her son Andrew even says that she always acts "like [she's] running for mayor of Stepford."
Doctor Who: Amy Pond shows signs of this at times, as according to Karen Gillan deep down she doesn't trust the Doctor as much as she seems to. Word of God says that in Amy's Choice the dreams were the Doctor's and Rory's and that she has no dreams of her own. Then there's the fact she has no memories of any reason to be in mourning after episode 9... And then at the end we find out why it was just her in that big empty house for all those years...
A slight case with Dr. Quinn, Medicine Woman's sister Rebecca, who seems almost hell-bent on being cheerful and seeing the good in everything. After a confrontation with her conversely bitter and depressed sister Marjorie, she admits to Mike that while she's not secretly unhappy, she's been expected to be The Pollyanna since childhood and sometimes finds it exhausting.
EastEnders has Vanessa Gold, a lovely, only slightly tarty woman with perfect hair, a perfect name, and a perfect complexion, wearing exclusively white. She smiles an awful lot, and allows herself to put up with a cheating husband for many, many years. When Max leaves her for Tanya, she goes a wee bit bonkers, including a lot of screaming, derpface and smashing living rooms, but the really powerful stuff was her obsessive cleaning when she suspected the affair.
Sansa is forced to become one to survive in the royal court in King's Landing. Even though she loves and is happy to see Jon, she has too many trust issues (thanks to being continuously manipulated by people over the course of six seasons) and can't completely open to him.
Gilly also uses it as a survival technique.
"Mockingbird" reveals that Selyse is not quite as okay with Stannis and Melisandre having sex as she's let on, staring at Mel's nude body in apparent jealousy and repeating her earlier praise of it almost as a Survival Mantra.
In Get Krack!n, the show's cosmetic expert seems constantly on the verge of suicide, and only keeps going through denial of reality and a completely unfounded belief in the life-changing properties of makeup.
In Girls, Marnie projects this trope when talking to her ex Charlie.
Audrey: Omg, are you one of those real housewives?
Girls5eva: Summer desperately maintains a cheerful front to convince the world she's happily married. The ruse is clear to everyone else, however.
Quinn tries this, hoping to hide her pregnancy from her family and the rest of the school and continue to play the part of the popular, celibate cheerleader, until such point as the truth becomes too obvious to ignore. It doesn't work — and when word gets out, she loses her popularity and even gets kicked out by her parents. And according to Quinn, her mom is one of these as well (what we know of her makes it obvious she's at least a Lady Drunk).
Quinn: And you just pushed it aside, like we do every bad feeling in this house. If you don't talk about it, it doesn't exist.
Episode 12 hints that Rachel might be one of those as well (especially the Lily Allen version of "Smile"), or might become one someday (when she tells herself that "it's Lonely at the Top" when Finn apparently abandons her when the Glee club is due their photos for the school yearbook).
Terri tried to be one of these with her fake pregnancy.
Blair is Depressed, especially during the first season when she's with Nate. Serena accuses her of being in constant denial in order to keep her life perfect. She admits to faking her happy sparkly persona to her stepfather in Season 4: "What kind of a princess schemes and plays sex games and drapes herself in old Hollywood movies?"
Also, Nate Archibald's mother. To the point of being called the Archibot by fans.
Lemon Breeland from Hart of Dixie is definitely Depressed and also leads an entire clique of oddly similar smilers.
Hambrosia Heartshe from The Heart She Holler is constantly smiling, even when she finds out unsettling information, such as that her husband is cheating on her with her sister, the town prostitute. After her HeelFace Turn, this is turned Up to Eleven, and she basically has a Joker Smile.
Lily from How I Met Your Mother did this at least twice: first she pretended to be happy coming back from San Fransisco when she was actually miserable, and second she tried to ignore all the disasters during the preparation for her wedding (her ex-boyfriend Scooter showed up trying to win her back, her veil got ran over in the parking lot, the pregnant harp player goes into labor,etc.) before finally breaking down at the last second.
On the Season 8 episode of Law & Order: Special Victims Unit, "Cage," Detective Beck — filling in for the undercover Benson — is looking after the sweetest little girl, who adores her caretaker. In fact, this bond is so strong, the girl sets Beck's couch on fire, in hopes that she and the detective will both die, so that they will never be separated.
Edna Bollington from the Kraft Suspense Theatre episode "Are There Any More Out There Like You?". Her family is collapsing around her; her daughter's college friends are a group of smug, heartlessJerkasses who have involved her in a fatal drunk driving accident, and her husband is angsting over it. Even worse, it's the holidays. Poor Edna doesn't know how to deal with all this, so she ignores it as best she can and concentrates on fixing the best Christmas dinner ever.
It depends on how you look at it but Valery Denton from The League of Gentlemen has to put up with a lot; a husband who is obsessed with toads and keeping the house clean, a pair of Creepy Twins who constantly appear at your side out of nowhere, and a hidden desire to have had a son ( one of the reasons for why she wants to keep Benjamin in their house) all the while smiling and not complaining.
Matron: And now, Zev, repeat after me: "Are you comfortable, darling?" Girl: "Are you comfortable, darling?" Matron: Very good, Zev. Your reading was an 8.3% deviation from standard.
Betty Draper from Mad Men could be used as a textbook example; she's playing the role of '50s wife and mother so perfectly that her impending nervous breakdown seems like a surprise even to her. It didn't help being married to Broken Ace Don Draper. The fourth season spent much time surveying the wreckage of that broken union.
The Man in the High Castle: Many of the housewives among the Nazi elite in the Greater Nazi Reich are implied to be purposely projecting a positive image to the outside world but are in fact scared both of each other and of being seen as subversive in any way. John Smith's wife can barely contain her anguish at knowing that her son would be killed by the state if his disability was revealed, and Juliana meets another woman among the group who is scared that she'll be brushed aside by her husband if she can't bear him children.
Barb Ballantine, the 'perfect' mom from The Mommies, showed signs of this trait.
Motive: Stephanie Carter, the killer in "Calling the Shots", who is mentally unstable and maintaining her suburban paradise by running a Ponzi Scheme and bilking her friends and neighbours. When the Victim of the Week threatens to bring her perfect life tumbling down about her ears, Stephanie kills her.
Nashville: Juliette Barnes doesn't spare anyone the snark and occasional jerk part of her Jerk with a Heart of Gold peresonality. She also occasionally smiles in this manner despite her life to make it look like everything is okay and thus shows several broken smiles during times when drama hits. She was brought up by a seriously damaged mother solo, developed a tough shell to get through her personal and professional life, is difficult to work with, has a truly heroic capacity for the demon drink, and did not take well to motherhood ("Gimme the damn baby!") to the extent of having to go into rehab. She also has a psychotic break towards a fan taking pictures of her, attacking her in a rage.
Julia McNamara from Nip/Tuck is half Stepford Smiler and half Defrosting Ice Queen. You have to have a little sympathy for the woman, as she has been keeping her son's paternity secret from both his natural father and assumed father. Unfortunately, her eternal struggle over "Sean or Christian?" just annoys most people.
Regina from Once Upon a Time is somewhat both Depressed (or least a Psychotic Smirk) and Unstable. While most of the characters (once the curse breaks anyway) recognize her as Depressed, only Arch-Enemy Snow White and possibly Jimmie Cricket recognize her as Unstable. Snow White even comments at one point that she is a deeply brokenwoman.
Alison from Orphan Black is a neurotic, image-obsessed soccer mom who hates her neighbors (to the point of doing nothing to help when one of them is dying in front of her, though she does feel bad about it afterwards), cheats on her husband Donnie, and has an enormous problem with the bottle. And that's before one considers the fact that she's a clone, and has to live with being watched and regularly "tested" by the people who created her (and think they have the right to own her) and being marked for death by religious fanatics who think she's an abomination. She gets better in Season 2, though, after being sent to rehab by Donnie after one alcohol-related mishap too many and reconciling with him soon after.
Being a spunky fifties parody, the gang from Pushing Daisies has met their fair share of this trope. For example, Hillary Hundin from "Bitches", Madeline McLean from "Corpsicle" and Mrs. Vandersloop from "The Legend of Merle McQuoddy". It's implied that Charlotte -Chuck-Charles is one of this as well. Specially when confronted with the issue of her own existence on "Bad Habits".
In Raven's Home, Chelsea seems pretty dang chipper for a woman who is now a divorced, single mother due to her ex-husband being arrested for tax fraud. Said ex also cheated on her, stole most of her money, and is implied to have been overprotective. As Raven realizes, Chelsea is actually keeping her frustrations pent-up inside her.
The fourth season premiere of Sabrina the Teenage Witch had Sabrina consider moving in with her father on her 18th birthday. Hilda and Zelda are devastated but cast a spell to give them big toothy smiles so as not to spoil Sabrina's birthday. The effect is slightly creepy.
Effy is a combination of Depressed and Unstable. Her random personality shifts in the previous series, from Silent Bob in Season 1 to Magnificent Bastard in Season 2 to Fille Fatale and Emo Teen in Season 3, were all various attempts at hiding it, some more successful than others (Season 1 and Season 3 both afforded some glances Beneath the Mask). In Season 4, the mask finally comes off.
Cassie in Generation 1 and Mini in Generation 3 are both Depressed. Cassie's mask comes off in Season 2; Mini's is gradually chipped away at throughout Season 5.
LanaLang becomes something like this around Season 6 when she marries Lex. It actually helped build her character, which was previously little more than Clark's Satellite Love Interest.
Chloe Sullivan borders on this towards the end of Season 8, after about two seasons of worse and worse Break the Cutie moments.
In the Shake it Up special Made In Japan, after a fight with Rocky and when her mom tried talking to her and makeup with her, "CeCe" smiley refuses as she was not only hiding her anger towards her but also how brokenhearted she was, although she didn't hid all of her true feelings as a side of her was glad it ended as she had enough of everyone around her not believing her side of the story and assuming that she was lying when she gives them the truth or half truth. However, they did makeup in end when they realize they need each other no matter the mistakes they make.
The Umbrella Academy has Allison, whose Establishing Character Moment is her smiling on the red carpet. We later learn that she's having a crisis over her misuse of her powers, is mid-divorce, has lost custody of her daughter, and is generally a mess. (And she's one of the more stable Hargreeves siblings. Yikes.)
V (2009): Anna is Unstable and her daughter Lisa is Unstable who later becomes Depressed.
WandaVision: Wanda is gradually revealed to be the Depressed kind throughout Episodes 1-4. She casts herself as a happy, smiley housewife and mother, but it's clear she has a lot of unresolved baggage regarding the events of the past and since coming to Westview has taken to actively blocking out anything that might compromise the domestic bliss she has created for herself. When a character on the Show Within a Show offhandedly references her brother's death, she realises she comes from outside the sitcom world and seethes with Tranquil Fury as she banishes her from Westview. She seems deep in denial of the fact Vision is dead as well.
The Wilds: Shelby definitely has shades of this at times. While she's genuinely cheerful and quite upbeat usually, this can come off as clearly forced when Shelby struggles with her anxieties over being a lesbian and the quite conservative Christian homophobia she had been instilled with. She breaks down over it briefly.
Lindsay is usually quite chipper, but her self-admitted skank tendencies and general immaturity don't mesh well with married life. As the series progresses, it's shown she is aware of the latter and doesn't know the first thing on how to survive as an adult and has a very low view of herself as a result. She goes through a lot of Character Development as time goes on, though it's not without a lot of trouble along the way.
Lindsay's sister Becca is arguably worse, as she seems to have married her Manchild husband Vernon simply for the sake of getting married, and is often shown to be rather unhappy but won't admit it for the sake of keeping up appearances. By the end of the third season, she even admits to the newly divorced Lindsay her jealousy of the latter's regained freedom and her fears that she's slowly losing her identity.
Gretchen suffers from clinical depression, and when it flares up, she goes past crippling sadness to just being completely unable to function. She's able to be quite happy and living well when it's not in full swing, but it's clearly shown to be a coping mechanism she developed to keep herself from losing her mind.
Spoofed somewhat in Season 6 of 24; after the father of one of Jack's unlucky girlfriends lampshades in graphic detail how bad things always befall Jack's loved ones, to the point of outright telling Jack that he's cursed and that he would never never be allowed near his daughter again as a result, Jack spends the last moments of the season breaking into the father's house and holding a gun on him, while ranting incoherently about how he's not cursed and ordering the guy to take back what he said.
30 Rock: Kenneth Parcell has shades of Depression. More or less confirmed in one episode when he flat-out admits to Jack Donaghy that he has to lie to himself in order to get through the day without cracking.
"Well, I'll tell you my secret sir! I lie to myself. Every morning, when I wake up, I say "everythings gonna be oookay," but I'm lying. And I don't know how much longer I can do it. (pained squeak as Kenneth resumes smiling) Have a swell night, sir!"
The android Ted was obsessed with reliving his creator's idea of a 1950s dream marriage, albeit with the aid of narcotics. (Though an android, he's chauvinistic enough to qualify.)
Spike himself also counts; despite all of his posturing as far as being a murderous badass vampire, with the body count to back up his swaggering, the dude is still the horribly insecure, Momma's Boynerd who writes crappy poetry, who overcompensates for his nerdiness by acting like a big time vampire. This was most notably shown in his origin episode, which contrasted Spike's boastful tales of past exploits with flashbacks that reveal how lame he used to be, right down to revealing that his nickname "William the Bloody" originally referred to his "bloody awful poetry."
He's both. The above would have him be something of a Stepford Snarker, but over the course of his Character Development and becoming a woobie he's also still an asshole. With codependency problems. He and Dru were groundbreaking for the series when introduced because they were very clearly people in addition to being monsters; Spike's whole character arc explores this. And messes with him for fun, apparently.
On CSI: NY Flack became one in Season 6 of the show after his girlfriend was killed in the Season 5 finale. Characters eventually started to guess something was seriously wrong, however, because he didn't keep the mask completely on all the time. Eventually, Mac saw through it and tried helping him, but Flack pushed him away. Eventually ended with Flack having a brief Heroic BSoD, finally letting Mac in, and eventually pulling out of it with help from Mac and the others.
Dexter: On the surface, Dexter Morgan affects a harmless, chipper personality to fit into society and hide the fact that he is a sociopathic serial killer. And empty. Over the course of the series, however, he becomes more in touch with his feelings and enjoys periods of legitimate happiness. Watching Dexter's face for real versus feigned expressions is very interesting, especially since the face you're watching actually belongs to an actor who doesn't mean the real ones or the fake ones.
The Fourth Doctor just loves to use smiling, happiness and bags of effusive personal charm to distract his enemies, companions and himself from thinking too hard about anything morally questionable he's being forced to do. He's certainly no stranger to proper gothicbrooding, but in situations where he's helpless to do anything and knows it, he responds with grinning and laughter. Sarah Jane even points out to him in one story that she can tell when he's lost control because he starts making more jokes and they stop being funny. Just a couple of the more notable scenes of this is him laughing to himself in his TARDIS after Leela leaves and K-9 is deactivated, and the amazing, hyper-enthusiastic way he announces to the people in the lighthouse that they're all going to die.
The Canon Discontinuity Shalka Doctor, much like the new series Doctors, was responsible for the destruction of Gallifrey. His recourse is being endlessly perky and singing showtunes, trying to avoid thinking about what he did as much as honestly possible (to the point that the Master serves as his reality check a lot of the time).
Nine: When his lone season started, he appeared to be manic and upbeat with a bit of rudeness mixed in and a small dark streak. Slowly, as more and more information about the Time War is revealed, it's shown that he is plagued by Survivor Guilt and searing self-hatred. This culminates in "Dalek", when he comes off as a Unstable during his terrifying verbal assault on the imprisoned creature. He gets better, though.
The Tenth Doctor acts bubbly and cheerful, cracks jokes in dangerous situations, and always smiles despite the odds. Underneath the optimism, however, he's frequently revealed to be suffering from various levels of acute mental instability. Ten did seem to be pretty genuinely happy up until he lost Rose. It all pretty much went downhill after that, culminating in "The Waters of Mars", in which his Stepford Smiler status is taken to terrifying new heights as he calmly and cheerfully explains to the captain of a destroyed interplanetary base that the lives of all her crewmembers are utterly unimportant to the universe, and that he'd only saved her life to prove a point. The woman is so disgusted by his attitude that she shoots herself, thereby saving the timeline of the entire human race. Which she wouldn't have done if he hadn't explained how important she really was back when he was leaving her to die.
Eleven is usually energetic, cheerful, and adorable as all hell. He also immediately recognizes that a villain is a part of his own subconscious because "there's only one person who hates me as much as you do", and, when presented with the (false) opportunity to find more Time Lords, was more eager about the chance to beg for their forgiveness than for companionship or a chance at locating friends. Then there's the scene when he's offered options for the TARDIS' voice interface. Himself? "Nonono, give me someone I like." Rose Tyler? "Oh, great. Give me guilt." Martha Jones? "Also guilt!" Donna Noble? "More guilt!" Finally, he says "There must be someone left in the universe I haven't screwed up yet!". Current companion Amy? Yeah, he thinks he's effing up her life too. Matt Smith actually described Eleven as a person who had to act happy and cheerful and put on a silly hat, otherwise he'd hang himself.
In a Doctor Who Magazine interview, Steven Moffat was asked if any of the Doctors actually liked themselves. He described several of them as this:
2: All that clowning, but oh that dark frown. Now, I'm just guessing, someone who play acts so much — do they like themselves? 4: You know what? I think he smiles too much. He moves too fast, and his eyes are too wild. And when that famous grin leaves his face, it's like winter in a moment. The Doctor is the angry old man of the universe, trying to kid you like he's just a clown in a funny scarf. 7: He may play the spoons, but there's a cold gaze fixed on you while he does. I think this Doctor would frown and look puzzled if you'd asked him if he was happy. "What's that got to do with anything?" he'd ask. And then he'd break into a gap-toothed grin, and spin his brolly till he made you laugh. 9: Oh, that wild grin. The one that tries too hard. There are moments when this Doctor looks so solemn, so dark and haunted, you just long for him to have a happy moment. And then he smiles, and you know just how bad it is.
The Master in his John Simm incarnation certainly counts as well. He manages to get himself elected Prime Minister of Britain, despite being both a homicidal sociopath AND a time-travelling alien. He's also disturbingly cheerful when discussing the fiery destruction of his home planet and all its inhabitants. He later spends the second half of a two-part episode trying (and succeeding, mostly) to bring them all back. This is particularly noticeable when, after receiving a phone call from the Doctor, his manic grin turns to a solemn frown, and the ensuing conversation is quite low key, especially when he discusses how terrified the Time War made him.
Euphoria: Although McKay appears to be pretty relaxed, he's actually got a lot of pent-up rage inside him. His father taught him to repress it in most cases, but he released it on the football field, until he reached college, where he was often benched.
Quite a few male characters from Game of Thrones could be interpreted as fitting this trope:
Tyrion and Jaime Lannister both smile and joke around a lot but they both also come across as being psychologically depressed behind closed doors. Even in later seasons, when Tyrion is obviously traumatized by the death of his lover and the events surrounding his trial — and when he is retreating into alcohol abuse — he doesn't drop very much of his fun-loving partygoer persona.
Prior to his capture by Ramsay, Theon epitomized this trope. He smiled constantly in the early series and is outward persona was that of a particularly giddy medieval fratboy, but his cheerfulness and outlook came across as unnatural, anxious and unrealistic. It was also deeply unsettling because (in real life) it would be practically impossible for somebody who grew up as a child hostage not to be severely traumatized by the fact, and because a lot of the more bizarre things he does and says closely match behaviors you'd expect from a teenager with severe complex trauma resulting from a long history of abuse. The logical conclusion here would be that Ned specifically groomed him to hide what modern people could only consider to be a horrific form of child-abuse. Even in Season 6, when he's way too messed up to smile at all, his sister calls him out on his "Theon Greyjoy impression", with the implication being that he still spends a lot of time pretending he is more functional than he actually is.
Ser Loras Tyrell is Depressed in Season 3. He puts on a charming smile and a pleasant disposition most of the time, but his mask slips at a very public event in "Second Sons", and his misery betrays itself more subtly in "Valar Dohaeris" (Loraswho is no longer paying attention to the dinner conversationhas a melancholic expression when King Joffrey says, "I'm sure she knows what she's doing"). In "The Climb", he sadly tells Sansa Stark, "It's [King's Landing] terrible isn't it? The most terrible place there is," which clearly indicates that Loras is suffering in silence.
Loras' father isn't given much screen-time but the character could also be interpreted as an example of this trope, since he is incredibly cheerful even when it makes no sense to the context. The in-universe explanation of his behavior is that he is not particularly intelligent, but given that he occasionally displays the briefest and most closely guarded expressions of shock/annoyance and, given that he's reasonably astute with financial matters, he's probably clever enough to have a basic understanding of what is going on.
Blaine from Glee is Depressed when we first meet him in the second season. He puts on a Big Man on Campus facade to impress Kurt and his friends in the Warblers, but it's a mask for his insecurities and his being haunted by his decision to transfer out of his old school instead of standing up to his bullies. He gets over it once he starts dating Kurt and transfers to McKinley, however.
Hannibal Lecter seems on the surface to be a kind, intelligent man. World renowned psychiatrist, expert cook, and works with the FBI on profiling psychopaths. Of course really he's the Chesapeake Ripper and is cooking up his victims for his gourmet dinner parties. A combination of Empty and Unstable.
And poor Will Graham also fits Depressed. His empathy disorder means he can empathizes with every criminal and murderer he comes across, and ends up with Garrot Jacob Hobbs (your friendly neighborhood cannibal who wanted to eat his own daughter) stuck in his head. He attempts to hide his issues, which are compounded by acute encephalitis that causes hallucinations, lost time, and a host of other problems with, while not a happy face, a decent mask. Thankfully he has his therapist Hannibal Lecter to help him. Poor guy.
Nobori Taiga from Kamen Rider Kiva: Friendly, polite and nice to his old friends, but secretly working to destroy humankind.
Eiji Hino from Kamen Rider OOO is one of the Empty kind. He is cheerful and always ready to help others, without showing any desire for himself. Other characters even explicitly call him empty. The fact he is devoid of any desire for himself is actually a major plot point, as this makes him the perfect host for the Purple Core Medals, which slowly turns him into a Greeed.
The eponymous Merlin seems to be The Pollyanna (albeit a very dark version), but he has his moments of this. Like this particular Tearjerker from 2x08.
Arthur: It has once again become clear to me that those who practice magic are evil and dangerous, and that is thanks to you. Merlin: (smiles with the saddest eyes you've ever seen) Glad I could help.
In Mr Selfridge, Harry Selfridge is a major example. He's always chipper around his family and staff, but he's also under a lot of pressure, and his marriage is falling apart. A number of scenes show him entering a room scowling, only to realize that he's being observed and instantly shift into a big smile.
Person of Interest: Elias smiles pretty much constantly in every scene he's in, that and the fact that he's a Magnificent Bastard makes it difficult to predict whether he's going to double cross whoever it is he's talking to or not.
Sherlock's Jim Moriarty is Unstable all over. He's got a lilting Irish accent, grins and giggles a lot, and then does a 180 and threatens to turn you into shoes... and then smiles.
Every male cast member fits this description. But most notably, there are Curtis "Lem" Lemansky (popular police officer and all around good guy who has ZERO self-esteem and basically serves as a doormat for his "best friends" on the Strike Team, leading to crippling ulcers, a mini-nervous breakdown, committing criminal acts that ultimately lead to his arrest, death, and ultimately denounced as a monster), Shane Vendrell (who loves his family to the extent that he murdered his best friend/partner rather than risk having him turn state's evidence against them, but basically murders his pregnant wife and toddler son rather than risk having Vic Mackey reveal to his children the sins committed by his father), Police Captain turned City Councilman and Mayoral Hopeful David Acaveda (affable but somewhat slimy boss who is into rough sex, arranged the murder of a man who raped him, strained relationship with his wife after being told by her that she would have preferred him being killed to him being raped, willingness to work with the Mexican Mafia and use their blackmail files of prominent people to further his career), Ronnie Gardocki (lovable nerd whose darkness manifests itself in full force in Season 7, by way of the lengths he was willing to go to see Shane Vendrell murdered as payback for Shane killing Detective Lemansky), and John Kavanaugh (brilliant and decorated Internal Affairs police officer whose devotion to law and order hides the fact that he cruelly divorced his mentally unstable wife the moment she became an annoyance to him).
Not to mention Vic Mackey, whose Stepford smile hides a monster that all others pale in comparison to. So it says something that in the end, Vic loses everything in the finale including his "good" name but ends up in the final scene of the series, putting on a Stepford smile and walking into the darkness, as far as not letting his karmic final fate as a glorified temp desk worker with the Feds slow him down.
Garak is both a Stepford Smiler and a Stepford Snarker. He's always amiable, cheerful, engaging and polite... and also very sarcastic. Midway through series 2, he suffers a life-threatening breakdown that reveals he's utterly desolate by his status, is living under torturous conditions (human norms make the station too bright and cold for a Cardassian) and can barely cope with how much the Bajorans on the station loathe him for being a Cardassian. After Bashir helps him recover, he returns to his amiable, cheerful, snarky disposition, but every so often episodes do dive Beneath the Mask to show the audience that his exile remains a source of great pain and loneliness for him.
Supernatural: If you know what's going to happen, Dean comes off as a version of this trope in the supposed lighter moments of Seasons 2 (the season where everything leads up to him making the demonic pact) and Three (when he has done so). Whether it's the Daddy Issues or Survivor Guilt or his impending death/suicide, he loves to pretend that everything is perfect when it's really, really not.
Played with, Season 7's episode 11 gives us this advice:
Frank: (to Dean) Here's my advice you didn't ask for: Quit. You want to keep going? You're going to drive yourself into the ground first. Do what I did when I was 26 and I came home to find my wife and two kids gutted on the floor. Decide to be fine till the end of the week. Make yourself smile because you're alive and that's your job. Then do it again the next week. I call it being professional. Do it right, with a smile, or don't do it.
Which leads us to the ending of the episode where Dean, as he's driving, tries to smile and utterly fails.
Happens twice in Season 6 during Sam's missing soul arc. First it's Sam wearing the mask, trying to pretend to have the human emotions and empathy that come with a soul, then when he gets his soul back, everyone else around him is wearing the mask to try and keep him from overthinking and breaking down the mental block keeping the traumatic memories/guilt from destroying his mind. Obviously, both of these masks fly off in spectacular fashion.
Klaus Hargreeves from The Umbrella Academy is constantly smiling, laughing, and cracking jokes. He's also a drug addict trying to cope with a childhood of abuse and the constant screams of the ghosts he sees.
Mixed Gender Examples
30 Rock has the Jessup family who takes this so far that their family crest is a knight refusing to talk about his feelings.
On Boardwalk Empire, Stepford Smiling is a way of life for New York gangsters Arnold Rothstein and Meyer Lansky. Rothstein smiles constantly — when he's amused, he smiles. When he's confused, he smiles. When he's irritated, he smiles. Even when he's chewing someone out over the phone, he smiles. You know the shit's hit the fan when Rothstein chews you out without smiling. Lansky picked up the smiling habit from his boss, though his are less unpleasant and more "can't we all just get along and make money"?
Among the ladies, the undisputed Queen of this trope is Gillian Darmody. She always smiles and acts cheerful to everyone to survive and get what she wants. She remains the concubine of the man who raped her as a child until she momentarily drops the act to enact her revenge. Even afterwards, she pretends that they're still good friends. In all other aspects of her life, she behaves as the smiling hostess even when she's talking gritty business and being outright threatening.
Chuck and Sarah always circle around this trope as they keep denying their feelings for each other and insisting that their relationship is "strictly professional". A most notable example was in "Chuck Versus the Breakup" when, after a heart-wrenching speech, Chuck becomes convinced that Sarah's feelings for him aren't real so he lies through his teeth saying he just wants normal and that Sarah "just can't be normal". It deeply hurts Chuck to say this while Sarah is extremely crushed and devastated that he would reject her. However, they both put on fake smiles and pretend to agree to his arrangement while preparing for Ellie and Devon's wedding.
Another example from Dexter; the Trinity Killer and his family. The family act like a perfectly happy, wholesome family while hiding the severe physical and psychological abuse they suffer. Trinity acts like a good man and pillar of the community while hiding that he is a brutal serial killer.
The Ood, as revealed in "Planet of the Ood". They appear to be happy and servile but are really sad shells of their former selves, having lost both their second brain and their psychic link to the group brain. In stories with the Ood set after "Planet", the slave Ood are partially restored, reconnected to the group brain, while the non-enslaved Ood have everything back.
Comedy example from Father Ted: the O'Learys, who behave like a perfect, arm-in-arm couple while anyone else is around, but spend the rest of the time hurling obscene abuse at and trying to brutally injure each other.
Monty Python's Flying Circus: Similar to the "It's a Good Life" example, the "Fairy Tale" sketch had the citizens of Happy Valley who were always happy and cheerful, because to be otherwise was a crime punishable by death.
Odd Squad: When brainwashed by President Obbs in "Oscar Strikes Back", all of the Scientists at Lab-Con wear very unnerving smiles, which isn't helped by their constant repeating of "Get Oscar! Get Ms. O!" Later on, both Ms. O and Oscar also wear unnerving smiles when they become brainwashed by Obbs as well.
Political Animals: The Hammond clan are all the depressed type. Elaine even blames it for her losing the presidential primary, since unlike her husband Bud, she doesn't believe in her speeches and is actually pretty misanthropic.
Gem and Gemma of Power Rangers RPM. The disturbingly cheerful smile never leaves their faces, whether they're talking about explosives, military strategy, their time imprisoned by the enemy and forced to do hard labor in an enemy factory producing Mooks...
They also love drawings of unicorns, butterflies, and rainbows, and work them into anything they write or draw (including a very, very confusing map to said factory, composed entirely of unicorns and rainbows).
The Rick Mercer Report invokes this in thisParody Commercial about Canada's Liberal Party. Though the particular parody ad involves a male character, it's used as a metaphor for issues applying both to male and female members of said party.
On an episode of Roseanne, David got a job at a theme park where all the employees (and soon David himself) are turned into Stepford Smilers. The Conners are thoroughly creeped out.
In "Number Twelve Looks Just Like You", Stepfordization is a standard part of becoming one of the beautiful people.
Most characters in Twin Peaks live this trope — it is one of the key fascinations of David Lynch and common in his work. The key theme of the show is taking a dreamy, perfect small rural town with white picket fences and exposing the hypocrisy, instability and literal evil that underlies it everywhere. Shades of grey abound.