In the episode "Her Parents", Jake disguises himself as a rainicorn by shape-shifting himself in order to have a long body and a horn, and painting himself in condiments. He's utterly baffled when Lady Rainicorn's parents fall for his disguise.
In "Morituri Te Salutamus", Finn tricks the Fight King into believing a mud statue he made was actually Jack.
In "Loyalty to the King", the Ice King shaves his beard and changes his name to "the Nice King" yet no one can recognize him.
Happens again in "Toddler Terrors of Time Travel", where Bowser and Kooky pretend to be plumbers in Brooklyn and intentionally clog someone's drainpipes.
Happens once more in "Send In The Clowns" (an episode of Super Mario World), where Mario and the cave people don't realize the clowns in Bowser's circus are actually Rexes until one of their noses falls off.
Subverted in "Reptiles in the Rose Garden" when the brothers try to sneak onto Bowser's ship wearing Hammer Suits. The first Sledge Brother they approach takes one look at them, and without missing a beat asks, "Putting on a little weight, aren't you, Mario?"
Double subverted in "The Beauty of Kootie". Kootie Pie's realistic human disguise fools Mario, despite her Cheatsy forgetting to remove her tail.
In "Rock TV," King Koopa sells televisions to the people of Dome City (plus Mario and Luigi) with the intention of hypnotizing them. He disguises himself as "Robby Rockwell" by putting on an obviously fake human head (there are bolts visible on it) and badly-fitting suit which does nothing to disguise his green, reptilian hands. Despite dealing with Koopa dozens of times, they fail to recognize him.
This goes all the way back to The Super Mario Bros. Super Show, the first animated Mario series. In "Count Koopula," Koopa's minion Mouser disguises himself in a black cloak that doesn't even cover his whole face, but no one is suspicious. It isn't until he slips up and calls Toad by name that anyone is even slightly aware of what's going on.
In American Dad!, people seem to recognize Roger as an alien only when he's stark naked. If he has so much as a wig on, he's completely inconspicuous despite his obviously non-human body.
In one episode, Roger gets in a hit-and-run accident wearing nothing but a wig, a wifebeater and Kevin Bacon's nose from a disguise kit, and Kevin Bacon gets blamed for it. Even Bacon himself is convinced:
Bacon[crying] I don't remember doing it... but it's clearly ME on the tape!
Steve's friend Toshi knows Roger's an alien, but of course no one understands him.
As does Bob Todd in For Whom the Sleigh Bell Tolls.
Bob Todd: Well, if it ain't an alien in a wig!
Also played with in the episode "Con Heir", when two FBI agents come to the Smiths' home looking for a man who is 6'2", 65 years old, sometimes leaps from a helicopter, has a salty demeanor and wears a turtleneck. Francine thinks they mean Stan's father until she sees the mugshot. In which he has a mustache.
FBI Agent: No mustache? Sorry to waste your time, ma'am.
In the episode "Flirting With Disaster", the Chinese spies infiltrating the C.I.A. are incredibly obvious; they just wear blonde wigs and make Suspiciously Specific Denials while asking for secret nuclear launch codes.
In "Stanny Tendergrass", Roger reveals that he has at least one disguise that each member of the Smith family is unable to see through. Stan doesn't realize he's one of the wealthy members of a country club he works at during the summer, Francine's is a Korean boy who plays with a giant chopstick, Haley's is her sandal repairman, and Steve's is Alicia Wilkner, a girl he went on seven (nine when including times Roger drugged him) dates with.
The "Chicken Boo" segments of Animaniacs are based almost entirely on essentially parodying this trope. Despite having the word 'chicken' in his name and usually being referred to as a giant chicken, Boo is a giant rooster that cannot speak and is not anthropomorphic in any way, besides apparently having opposable thumbs. However, the flimsiest of disguises will cause everyone except one person to treat him as an expert in whatever field he's chosen to enter, be it acting (a French-style mustache), karate (a white uniform and headband), or even the Confederate Army (a gray hat). The single individual who realizes the truth desperately tries to point out how painfully obvious the disguise is, but everyone else will simply laugh or take that individual to be speaking metaphorically. When Boo's rooster mannerisms inevitably come out (such as trying to eat a grasshopper or being upset by the sight of fried chicken), he panics and loses the disguise, which suddenly makes everyone realize his true identity and form an angry mob to chase him off, while the Cassandra returns to gloat ("I TOLD YOU THAT GUY WAS A CHICKEN!").
Theme Song: You wear a disguise to look like human guys, but you're not a man, you're a chicken, Boo.
In other Animaniacs cartoons, however, this trope is often played straight. Characters are often completely fooled by when one of the Warners puts on a disguise and an accent.
Subverted pretty regularly in Slappy Squirrel's segments. Her opponents often resort to this (Among other stock cartoon tactics) to try to get the better of her, but she's so Genre Savvy she sees through them right away.
In one, Daniel Boone tries to dress as a bird to get at Slappy's tree, but the disguise is "pretty absurd" (as the chorus acting as the Interactive Narrator clearly says) and Slappy doesn't fall for it.
It's pretty easy for Slappy herself, however. In one cartoon she is able to fool two movie critics who gave her old cartoons a rather cruel review (Expys of Gene Siskel and Roger Ebert) simply by wearing an usher's uniform and then switching to a popcorn vendor's uniform in the next scene.
In Avatar: The Last Airbender, the kids' disguises include Aang wearing a wig and moustache made of Appa-fur and pretending to be an old man, and Sokka and Katara donning a moustache and fake baby-bump respectively and pretending to be Aang's parents. They are two and three years older than Aang and have much darker skin. Completely believed every time.
It seems that all Aang ever has to do is cover up his arrow, and he's safe. Eh? That kid with a turban has the same yellow and orange garb as the Avatar? Well phooey, we can't see his arrow! There's no way it's him!
Though, admittedly it got a lot better in the beginning of Season Three, what with completely different clothes, actual hair, a headband, and an attempt to assimilate.
Also, it seems like people generally don't know his appearance that well... after all, there's no photography in this world - all they have is colorless drawings, and that's only in the Fire Nation.
It makes sense with Katara and Sokka most of the time because (for whatever reason) the Fire Nation never made wanted posters for them. Even then, the Water Tribe ethnicity is pretty visible (darkest skin of any group in the 'verse, for a start) and the Fire Nation is at war with both tribes.
In the episode "Sokka's Master", at the very end Piandao reveals that he always knew Sokka was a member of the Water Tribe, since the name "Sokka" is very distinctly Water Tribe in the series. He recommends, for future reference, the name Li. "There's a million Lis."
Also Zuko and Iroh while on the run from the Fire Nation in season 2. Despite being on hundreds of wanted posters throughout the Earth Kingdom, no one ever manages to recognize the angry teenage boy with a huge scar traveling with his short, chubby uncle as the two fugitives on the poster.
Or, from a Fridge Horror perspective, an angry teenage boy with a giant burn scar on his face living homeless with an elderly uncle could actually be pretty common.
In season 3, "The Painted Lady" this trope is both subverted and averted. Katara dresses as a Spirit to help a town who's river was polluted by the Fire Nation's factories. It's actually quite a brilliant disguise, and with the help of her waterbending, she's very convincing (at least until Aang catches her sneaking off). On the more comedic side, we have a man who seems to be completely insane. He switches hats and names, telling the gang he's a trio of brothers.
"Xu": I'll get my other brother, Bushi! He loves cleaning rivers! (removes his cap, a straw hat flops out from under it) Okay! I'm Bushi!
Aang: I knew it! You are the same guy! You just switched hats and called yourself a different name!
"Bushi": Oh you know who does that? My brother, Dock. He's crazy.
In an episode of The Backyardigans, Pablo self-proclaimed himself as "Le Master of Disguise" (which just happened to be the episode's title), and he couldn't be recognized by any of the other characters, most especially when he dressed up in the costume Austin was wearing at the episode, mustache and all (though Pablo's was over his beak), and the others couldn't tell them from each other, even if Austin (a purple kangaroo) and Pablo (a blue penguin) looked nothing alike.
Batman looks and sounds the same as Bruce Wayne, but aside from Wonder Woman and Ra's al Ghul, very few people in the DCAU seem to notice the resemblance.
In most of his incarnations, Batman's voice and body language are very different from Bruce Wayne's, and Wayne makes himself too big of a fop to be taken seriously. But one wonders why it isn't obvious to everyone besides Ra's Al Ghul that he funds Batman's operations, since he's the richest man in the city, and the only one with unlimited access to the kind of technology Batman routinely uses.
Wayne's not the only game in town when it comes to rich people with advanced toys. By that standard alone, Lex Luthor and Vandal Savage are also likely candidates.
Neither Luthor, nor Savage are lifelong Gotham natives who watched their parents be gunned down in an alley.
He further covers his back when explaining to his mechanic he has "backers" with dummy companies funding his crusade. Which does bring back the question if Bruce Wayne is one of those backers.
Commissioner Gordon somehow fails to recognize his own daughter, despite the fact that the mask doesn't even cover her eyes, nor does she use a different voice.
One version implies he does know and is a Secret Secret-Keeper because things would be difficult otherwise.
However, in "Never Fear," Wayne reprises his Matches Malone alias, but looks exactly like Wayne in his standard TNBA business suit, and wearing a pencil thin moustache and possibly sunglasses. None of that wardrobe and make-up artists' effects seen in "Shadow of the Bat."
The Beavis And Butthead episode "Pool Toys" has the duo wear nerd glasses to try to fool Tom Anderson into getting them to build his swimming pool. Were it not for Anderson's poor eye sight, this plan probably wouldn't have worked.
In an episode of Beetlejuice, the main character is competing with a guy named Germ Pondscum for the title of best prankster - and is lagging behind. When he goes to a store to buy supplies hoping to score more points, Pondscum is the clerk, disguising himself with nothing more than a set of novelty nose-and-glasses. (Naturally, what he sells BJ gets him in big trouble.)
An episode of the 2006 revival of Biker Mice from Mars called "It's The Pits" has Dr Karbunkle wear a fake beard in some scenes.
In the episode "I Oughta Be in Toons",Lucky Piquel is the only one deceived by Babyface's Mickey Mouse disguise, somehow not noticing that Babyface is tall, obese, and looks more menacing than the real Mickey.
"Cereal Surreal" has the Wheat Crunchies mascots Slap, Sniffle, and Pop being framed for stealing decoder ring prizes from their own cereal boxes by their would-be replacements Turbo, Banshee, and Kapow, who wear masks with clearly visible seams on them.
"A Fine Kettle of Toons" has Lucky successfully impersonate Fall Apart Rabbit even though Fall Apart is a short toon rabbit and he is an overweight human.
Bugs Bunny can pretend to be a human by simply wearing human clothes. This cover is usually blown when someone notices his tail or ears. Of course, no one bothers to notice the gray fur or obviously non-human face...
In "Forward March Hare" (1953), the sergeant-demoted-to-private only notices the ears pretty far along, and then mentions the fur before realizing the Army's inducted a rabbit by mistake.
In "Bowery Bugs" he impersonates several different people from a swami to a police officer, all by just changing clothes. When the villain of the short finally catches on, he mistakenly thinks that everyone is turning into rabbits, goes insane, and hurls himself off the Brooklyn Bridge.
During the "hunting trilogy" he impersonates everything from a woman to the Game Warden, Elmer is fooled every time.
An episode of Tiny Toon Adventures did the same thing in an episode where Babs Bunny pretended to be a human simply by dressing like one so she could star on a teen drama. It was even lampshaded when the makeup guy told her she should consider getting a facial wax to remove excess hair. Why the various other times the species of the characters didn't matter to other humans (including the ones that went to school with them, aside from Elmyra) is ignored.
In the Looney Tunes short "Dough for the Dodo", Porky Pig fools the Dodo by wearing only a ragged green coat and an umbrella on his head. However, in the original short "Porky in Wackyland" (which was the former was a remake of), Porky had a very effective disguise wearing a false beard that covered everything but his eyes, a false nose and glasses, a different coat, and a helmet with a light bulb on it.
Another Looney Tunes example, though this counts as a subversion: In "Dog Pounded", Sylvester puts on a dog suit to infiltrate a dog pound where Tweety is hiding. So unconvincing is this disguise, that the dogs inside see through it immediately and attack, forcing Sylvester to make a quick escape. Later, a Double Subversion occurs when a dogcatcher notices the still-disguised Sylvester and inattentively throws him back into the pound, where another mauling awaits.
Bugs explained this phenomenon himself to Buster and Babs in the first episode of Tiny Toon Adventures: "Eh, you'll be fine if you remember t'ree things. One, your adversaries have tapioca for brains. Two, always eat your carrots. And three, villains always fall for cheesy disguises." The last line was said while briefly disguised in a shabby-looking Taz costume (which still manages to scare Buster and Babs). The next scene (at Montana Max's) has Babs recall what Bugs said about cheesy disguises, and the two dress up as Yosemite Sam (Buster) and Elmer Fudd (Babs) to fool Montana Max.
Bugs Bunny is so notorious for flimsy disguises that somehow work that, if this trope was up for a re-naming, "Bugs Bunny Disguise" would be an excellent choice.
Subverted in one cartoon when a watchdog is trying to protect chickens from a nearby fox. The fox trims the hair on his face and tail to masquerade as another dog wanting a job. The watchdog sees through it right away, but he decides to play dumb and puts the fox through hell.
In Merlin the Magic Mouse, upon learning that the sole person in the audience is a cat, Merlin hides the fact he's a mouse by wearing a mustach. The cat is fooled until it falls off.
Subverted in Hollywood Daffy, when Daffy tries several disguises to get past the guard, but none of them work.
Played with in Tortoise Wins by a Hare. In an attempt to learn how Cecil Turtle has been able to beat Bugs at every race, Bugs dons a disguise consisting of a long grey beard, sunglasses, and a hat (which he hides his ears inside of), and Cecil gives him information. But it turns out Cecil knew all along that it was Bugs, and was merely tricking him.
Also subverted in Backwoods Bunny, when Bugs is pitted against a dimwitted hillbilly buzzard. At one point, Bugs pulls his old dress-in-drag routine, and initially, it appears to work until the buzzard reveals that he wasn't fooled in the slightest.
Mr. Bumpy, the main character of Bump in the Night, occasionally used shoddy disguises.
"A Penny for Your Thoughts" had Mr. Bumpy at one point try to stop pennies appearing whenever he thinks by diverting their attention with a cardboard cut-out of himself while wearing a cowboy hat and a fake mustache.
"Love's Labor Bumped" had Bumpy learn that Destructo has a crush on Molly Coddle and decides to mess with him by impersonating Molly. His disguise consists of little more than a cheap wig, a glove mimicking Molly's right arm, and a red and white legging like the one Molly wears on her left leg.
"Not a Leg to Stand On" had Mr. Bumpy get in trouble when Molly Coddle thought he stole her feet, unaware that his intention was to give her new shoes. He attempts to lie low by disguising himself as Squishington's Cousin Bela, which had him wear a feathered hat, fake eyebrows, a fake mustache, and a fake blue nose.
An episode of Camp Lazlo had Lazlo, Clam, and Raj sneak into the Squirrel Scouts camp with Lazlo and Clam dressed as girls and Raj disguised as a log. None of the Squirrel Scouts seemed to notice.
In another episode the Beans Scouts fool the Squirrel Scouts by saying they have a unicorn which is actually a filthy disgusting llama with an ice cream cone on his head, later when they take the cone off they proclaim "He's hideous!" despite finding him beautiful earlier.
In Care Bears: Adventures in Care-a-Lot, many of the characters can only pull off this kind of disguise- resident villain Grizzle's disguises are often paper thin, and Funshine did it once to weasel out of being bedridden due to being ill. And the bears fall for it every time.
Amusingly subverted in Chowder; in an escalating effort to convince Panini that He's Not Her Boyfriend, Chowder turns up on her doorstep wearing a large black moustache and fabricates a story about the "real" Chowder moving far away and then switches gears to say that "Chowder's dead". Panini still knows it's Chowder, though. In the end, he foils himself after he gleefully accepts the cookie she offers him.
Inverted on The Cleveland Show in the episode where Roberta dons a Fat Suit. It's a very convincing disguise and almost everyone is fooled, but somehow Cleveland, Donna, and Rallo see through it.
On one episode of Clone High, the clone of Joan of Arc had to dress as a man by wearing a fairly obvious fake moustache that nonetheless fooled all of the other characters, because the basketball team wasn't allowed to include girls or animals. When her disguise is penetrated, her place is taken by a dolphin in an equally fake moustache.
Mr. Boss ridicules the Toilenator by mentioning that he was once fooled by Numbuh One in disguise, even though the disguise consisted solely of a T-shirt that said "I am not Numbuh One." (Of course, the Toilenator isn't all-too bright...)
In Operation: C.H.A.D., Mega Mom and Destructo Dad's full-head helmets pretty much resemble exaggerated versions of their actual faces, and don't hide their voices at all; yet, for some reason, this is enough to conceal their identities from their own son until they remove them.
And in the KND crossover with The Grim Adventures of Billy & Mandy, The Grim Adventures of the KND, Numbuh One's tomato-nose Billy disguise is intended to fool Billy's dad... but fools Grim before Dad can even get home. And when Mandy disguises herself as Numbuh One with his sunglasses and shirt, she fools the entire KND organization and takes over!
And changes the name to "Mandy", no less.
Numbuh 4-30teen-7 manages to get into a girl's slumber party. Though since the show itself would lampshade and subvert tropes, it's debatable that the girls may have known all along and merely acted surprised when his obvious wig fell off (they're supposed to be Genki Girls in general, closet or otherwise, but maybe that would be the point of their apparently not seeing through the disguise, rather than having IQ levels stereotypical for that).
It's unlikely that the girls knew all along-they seemed genuinely surprised when Numbuh Four's wig fell off. Plus, Numbuh 86 clearly didn't want to invite any boys.
Danny Phantom. This is even commented on in the "Ultimate Enemy" special. Dark Danny has Danny's family and teacher tied up and reveals who he is. He then asks them why they never noticed that "Danny Fenton" and "Danny Phantom" were so similar.
Played with in "Adopt-a-Con", where Tuskernini is able to fool others when dressed as Megavolt and Bushroot, despite being much more overweight than them. Darkwing Duck isn't fooled by the Megavolt disguise (and it's unclear if the tied-up guard is), while DW, Launchpad, and Gosylyn all know in advance that he's going to be disguised as Bushroot. However, those unaware don't know that he's really Tuskernini. The judge only finds out after he sees the flower pot used as hair fall off.
Whenever Quackerjack wears a disguise (such as a psychologist in "Days of Blunder" or a surgeon in "Stressed to Kill") he wears his signature jester mask, which he is rarely seen without. One would think he'd be less likely to be recognized without it.
In "Stressed to Kill" both he and Megavolt wear doctor outfits over their usual clothes. Darkwing is suspicious but since he's spent the episode overreacting to stuff because of his stress level they're able to convince him he's just seeing things.
Whenever Launchpad dresses as Darkwing, others get fooled in spite of Launchpad having a much bigger build.
The Dark Lord Chuckles the Silly Piggy in Dave the Barbarian has been known to dress up in all manner of costumes that somehow fool everyone, even though he's still very, very obviously a talking pig. Once he even introduced himself as "The Dark Lord Chuckles the Silly Music Producer" and still everybody was fooled. It's especially bizarre because the plot to one entire episode is predicated on his Amulet of Hogswineboar letting him project a physically perfect illusion of the title character's father, meaning that he's entirely capable of creating more effective disguises, he just chooses not to for some bizarre reason.
One episode had a Villain Team-Up get foiled by the heroes simply wearing papier-mache masks of said villains and insulting the other villains, making them turn on each other. One of the villains was Chuckles, who is the size of a regular pig and thus much shorter than a person. Another was Quosmir who is not only gigantic, but has the lower half of a snake.
In "Nuclear Confusion", Dexter poses as a stuffed swordfish by clenching a poker in his mouth. Of course, his dad doesn't notice anything.
Another one had Dee Dee accidentally shutting down the lab and spending the entire episode tricking Dexter into thinking nothing is wrong by impersonating Computer, Robot, and Mandark. Somehow this worked and Dexter is none the wiser. "Boy genius" my ass.
In another episode, Dexter grows a beard, which causes everyone to mistake him for the TV hero Action Hank. For reference, Hank is a tall, muscular black man, and Dexter is a nerdy red-headed boy who's portrayed in-series as being about two feet tall. The justification seems to be that nobody in the world except Hank could possibly grow a beard that rugged. When they meet, Hank himself even takes to calling Dexter "Little Hank".
Thug 1: Two Action Hanks!. Thug 2: But which one's the real one?.
"Momdark". Mandark kidnaps Dexter's mother and dresses up as her. His disguise is actually quite good, except for the huge glasses on his face (which she doesn't wear) and his voice, which doesn't sound like hers at all. However, it fools Dexter, Dee Dee, and their father completely.
In Dofus, Crocosec has the ability to disguise himself as anyone using anything. In his introductory episode, he disguises himself as a human kid (he's a crocodile) just by putting on a tiny hat. The disguise is so convincing that even his own allies somehow don't recognize him.
Subverted at the end of Don't Give Up the Sheep, when Sam clocks out, he instantly notices that the sheepdog who clocks in to replace him is Ralph in a very convincing sheepdog disguise and beats him. Though it could be he regognized the voice when he greeted Sam.
Drawn Together has this in "Mexican't Buy Me Love" where Ling Ling plays a verrrry convincing fighting rooster...with nothing more than a fake beak.
Averted on Doug when Skeeter tried to go to the Honker Burger in disguise after running away from home. Everyone recognized him right away.
In DuckTales, no one ever recognizes the disguised Beagle Boys under the fake mustache (or whatever), even though they always wear their robbery masks and prisoner numbers. Considering even their own family hasn't seen them without the masks, simply removing them might be far more effective than anything else they could do.
In a (non-DuckTales related) comic story, this is lampshaded by the Beagle Boys ridiculing one of them when he pulls off a disguise that's actually somewhat more convincing than most others, since he actually bothers to make the mask less noticeable by wearing huge glasses. Earlier and later in the story, the other Beagle Boys had worn disguises that didn't even cover any of their faces.
Evil The Cat tried this twice in Earthworm Jim. Oddly enough, it failed miserably in one episode (Evil took four Super Blaster shots to the face, once for each failed costume) and worked perfectly in a later episode.
And in the times that his disguise did work, he'd introduce himself by saying, "I am (whatever I'm disguised is) and not a cat. I'm here to (do whatever it is I want you to think I'm doing). And did I mention I'm not a cat?"
Psycrow and Professor Monkey-For-A-Head also managed to steal Jim's suit by disguising Psycrow's ship as a Laundromat (as in, just hanging up a sign saying it's a landromat and NOT Psycrow's ship.) Inside was the Professor dressed as a cowboy with a fake mustache and gigantic hat to hide the monkey. When a banana peel falls out of his hat, he just blames it on head lice.
Jim himself also manages to hide from a killer robot inside his suit by attaching himself to a wall and proclaiming "Hiss hiss! Hello! I am a steam pipe. The intruders went that way! Hiss hiss! Steam!"
In the episode "From here to Ed" in Ed, Edd n Eddy, the Eds manage to sneak past Kevin by disguising themselves as Jonny. Which means all three Eds are crammed into a gigantic papier-mâché sphere vaguely shaped like Jonny's head, with the eyes cut out and all three Eds plainly visible inside and an imitation Plank glued to the side. Kevin doesn't seem to notice, saying hi to "Jonny" and muttering "What a freak" when "he" hits the fence and falls over it.
In the episode "Laugh Ed Laugh", due to an epidemic, there are no kids for Eddy to scam causing him to eventually go completely insane. Ed and Edd attempt to capture him for his own safety and approach him by wearing badly drawn masks of Jonny and Plank. Ironically Eddy falls for the disguises even when Ed's mask FALLS OFF! Eddy thinking "Jonny's" face has fallen of assures "Jonny" that he will get him a new one.
Eddy: Hi Plank! [Ed is wearing a Jonny mask, and Edd is disguised as Plank.] Hi Jonny! I'd invite you in, but I just shampooed the rugs! [Ed's mask falls off which causes Edd to Face Palm] Ed: Oops. Eddy: Jonny. You dropped your face... I'll get you a new one!
In the episode "Pain in the Ed," Sarah instructs Jimmy to keep an eye out for Ed and to let her know if Ed isn't practicing his violin or if the violin breaks. As a response, Jimmy comes up with many disguises to wear while spying on the Eds. Said disguises are the following: a baby in a stroller, a bird in a tree nearby, being Mary and having sheep nearby, and a bunny (when Edd accidentally breaks the violin). Edd and Eddy are able to see through the disguises, while Ed, unsurprisingly, isn't. This prompts Edd and Eddy to make the destruction of the violin look like a complete accident.
In the episode "Pick An Ed," Eddy goes undercover as a new student "Carl." Edd is the only one able to see through the disguise while Ed (well being Ed) doesn't. The disguise immediately fools the other kids. This is played more straight when Eddy disguises himself as a female student named "Suzette." Plank is able to "see" through the disguise and Kevin exposes the disguise at the near end.
Eek! The Cat once featured "famous" performers, the Squishy Bearz, being framed for robbery by four rats wearing a Paper-Thin Disguise. How bad was it? One was just wearing a cardboard box with a smiley face on it and another had a large sock over his head. Done again in the same episode when the Squishy Bearz, on the run from the law, were forced to disguise themselves to avoid detection. Among the costumes worn: A grass skirt and coconut bra combo which really didn't cover the face at all. The people in the local diner didn't recognize them until a news broadcast showed how the Squishy Bearz might look in disguise, showing the exact costumes that they were wearing. Hilarity ensued.
Subverted in El Tigre with Sergio's disguise as his villain alter ego Señor Siniestro. It's actually a very convincing disguise and he's able to fool Manny and Frida. His habit of fawning over Frida is the only thing that could give him away.
Played straight when White Pantera infiltrates a supervillain's tournament. His 'disguise' consists of wearing a black suit instead of his usual white one and calling himself Black Pantera. Nobody is fooled, but play along with it anyway.
Cosmo and Wanda from The Fairly OddParents! have passed, floating and all, with signs that read "Normal" and "Human", respectively. They don't even bother with a disguise at a comic convention, as everyone assumes they're wearing costumes.
This happened again when Cosmo was being taken to the doctor. His main disguise is a green lamp with the words "Not Cosmo" written on him. This was only made worse by his line "A LAMP!!! The perfect disguise!"
Timmy's had a few, but the disguise in "Shiny Teeth" takes the cake: by simply wearing a tiara, no one, neither his enemies or a friend he has rescued before, can recognize him.
"The buck teeth look familiar but the tiara leaves me baffled!"
In "Love at First Height", Chester and A.J. put on a 'tall kid kit' to pass themselves as someone tall enough for the roller coaster. When their fake moustache fell the first time, Timmy's parents were the only people to see it and didn't suspect a thing. The second time, however, was witnessed by smarter adults.
The Crimson Chin wears a suit and glasses. Never mind that his super hero suit is worn underneath it—including his face mask. In fact, his suit seems permanently attached to him, as he's never seen without in even wearing civilian clothes.
In the episode, "Christmas Every Day", when Timmy catches up to the Lesser Holidays, he gets onboard their bus by disguising himself as "Birthday Boy", which merely consists of him wearing a candle on his head instead of his trademark pink hat.
Timmy: "Pssst! Cosmo! Wanda!"
Cosmo: "No, Timmy has a pink hat. That's Birthday Boy!"
Subverted in an episode of Family Guy: Peter is at the supermarket and partakes in a free sample, saying that it was quite good. Afterwards, a man identical to Peter wearing a Groucho Marx disguise takes a sample, then another Peter with a thin mustache and oriental haircut (plus a horrible Japanese accent). The employee informs him that he doesn't have to disguise himself to get free samples. Suddenly, Groucho Marx Peter and the actual Peter walk up behind him and ask if they can have another free sample.
Also in Family Guy, all it takes to be completely indistinguishable from the real Lois is to wear a green button-down shirt, beige pants, and orange wig. It is not necessary to fake the voice, the body shape, the ability to walk... Even just wearing her shoes, earrings, and lipstick is enough to confuse people, if not convince them.
In one episode, Brian tries to avoid Stewie over some unpaid debts. To try to sneak past him, Brian dons an elaborate mustache, and just that. He does manage to make it past Stewie with only a "good day sir" at first, but Stewie catches on after the double take.
There was the one where Peter went to his high school reunion pretending to be a space cowboy but one guy didn't believe him because his hat comes right off. A similar gag was done in "Road to Germany" when a Nazi found out Mort wasn't a priest by removing his collar.
In addition, Old Man Herbert attempts to disguise himself as a preteen to sneak into Chris's school dance, for obvious reasons. Even Brian, one of the smarter characters, is fooled, calling Herbert "one ugly eighth grader."
In another episode, James Woods returns to take revenge on Peter for breaking off their friendship. He does this by stealing Peter's wallet and dressing like him, then claiming that because he has his driver's license and credit cards, he must be Peter, forcing Joe to arrest the real hero and kick him out of his own house. Peter turns the tables by getting a few fake I.D.s of his own and going on a talk show as "James Woods." Despite clearly being an obese Rhode Island man and not the lean, suave James Woods, everyone is somehow fooled into thinking Peter is the actor.
In the first episode of the series's revival, Peter schemes to get into Mel Gibson's exclusive high-end suite at the new Park Barrington Hotel in New York. To do so, he puts on a ball cap and sunglasses, turns his collar up, and claims to have "put on a few pounds" for his next role. The clerk immediately buys it and escorts him and Lois to his room, although a few more Genre Savvy priests later catch on.
In "Peter's Daughter," Peter starts being overprotective towards Meg due to a near-death experience the latter suffered. In a scene when Meg and Michael are dating in a restaurant, Peter wears a disguise composed of the following: buck teeth, a straw hat, funny-shaped eyebrows, and two beards under his balls-shaped chin. He also fakes an accent. Neither Meg nor Michael buy the disguise.
One example is disguising himself as an old lady in "Into Outer Space" and disguising himself as King Neptune (by simply wearing an obvious fake beard) in "Blubberino the Whale".
In "Felix and the Mid-Evil Ages", when he sets up a trap to lure Felix into a Time Machine disguised as a photo booth, he doesn't even try to disguise himself aside from wearing a red cap—and Felix falls for it anyway! And once they reach the Middle Ages, Professor disguises himself as a king, but he blows his cover to Felix by chastising Rock Bottom by name.
In "The Professor's Instant Changer", he builds a hologram device that disguises himself as a rosebush (which Felix squirts a fire hydrant at, thinking the bush needs water), a pine tree (which gets struck by lightning from a subsequent rainstorm), and then a lawn chair (which Professor quick changes into a cactus when Felix tries to sit on it) but his limbs and mustache are still visible.
In "The Magic Bag", Felix manages to fool one the Professor's robot by turning his tail into a big mustache (which he calls "My Professor disguise!") and making his voice sound more hoarse.
Subverted in the Foster's Home for Imaginary Friends episode "Impostor's Home for...Um...Make-Em-Up Pals". A human-like "imaginary friend" moves in wearing just a clown nose and neck tie, and everyone is convinced but Frankie, who tries in vain to tell everyone he's an impostor; it turns out he is, as the clown nose is hiding an elephant trunk underneath.
Played with in the same episode where Frankie tests the friends' gullibility by dressing in her own "imaginary friend" disguise, which the friends fall for, but Mac and the alleged impostor see through it, and Bloo remains convinced that Frankie and her alias are still separate people.
In the episode “Frankie My Deer,” Mac, Bloo, an Imaginary Prince Charming, and a pizza delivery nerd attempt to use a fake disguise as a tall man to spy on Frankie on her date. Due to Bloo being the “head,” it was very obvious that Frankie wasn’t going to buy the disguise.
We see a video recording of customers in an alien sex shop. One of the clients (who is obviously Lrr in a ball cap and sunglasses) tells the clerk he's "just some guy...RULER OF THE PLANETOMICRON PERSEI 8!!"
And when the Decapodians declared war on Earth, and Zap Brannigan couldn't spot their spy, "Hugh Mann", despite suspecting his loyal assistant Kif (Kif seemed to be able to see through the disguise, but didn't say anything, probably because he never gets listened to anyway).
In "The Bird-Bot of Ice-Catraz", Bender is able to disguise himself as a penguin simply by squatting and putting on a tuxedo.
This is played with in the episode which introduces Flexo, the robot who's identical to Bender save for a small metallic "goatee". In a scene, we see what is clearly Flexo trying to pass up as Bender by wearing scarves and other items of clothing and referring to himself almost literally as "Not Flexo, but Bender". Later is revealed he was actually Bender all along and was wearing that clothing because of fashion sense.
When Fry and Leela visit a robot planet, all they need to blend in perfectly is to wear metal containers and pots.
Cubert Dwight and Tinny Tim were able to steal from Fry and Bender's apartment in plain sight of Fry by wearing crudely drawn Bender masks... all three of them at the same time.
In "Calculon 2.0", Calculon wears a mustache to audition as an unknown actor. Keep in mind that Calculon is a brightly-colored robot.
The Garbage Pail Kids Cartoon episode "Chris Messin' August" had a bratty kid named Chris Mess try to ruin Christmas for everyone by impersonating Santa Claus and convincing all the children that they now had to be naughty if they wanted presents. Somehow, nobody notices that he's clearly a child, he isn't wearing his fake beard properly, or that he has a burglar's eyemask.
Parodied and inverted in Garfield and Friends, with Orson wearing nothing but a moustache and costume posing as the Rooster Ranger to play a trick on Roy. Roy immediately recognized it as "Orson in a pathetic disguise", but when Orson fell into his mudhole Orson came up to investigate. It turned out that the Rooster Ranger was actually Lanolin in costume.
In another episode, Roy was hosting a game show where the audience had to call in and guess the mystery guest. The guest was Garfield wearing a Lone Ranger mask. Orson complained that anybody could clearly see who it was, but nobody got it right, not even Jon.
In "Binky Gets Cancelled Again!", Binky the Clown's show is replaced by the Buddy Bears, a Tastes Like Diabetes group that agrees about everything. Garfield decides to help Binky (largely because he finds the Buddy Bears even more annoying than the clown) and goes down to the TV station to speak with the Bears. When this fails, he decides to force them to disagree and destroy the show's credibility. Garfield does this by putting on a chef's hat and apron and speaking in an Italian accent, pretending to be a caterer. Somehow, this completely fools the Buddy Bears—even though they spoke to Garfield five minutes earlier.
In another episode, an ice cream man is giving out free popsicles to children in a park. Garfield stands next to his cart and puts on various wigs and hats to disguise himself as different kids. The ice cream man gives him dozens of popsicles, somehow missing the fact that Garfield is a two-foot tall orange cat covered in fur.
Another episode which parodied Barney & Friends saw a gigantic Tyrannosaurus rex (who dodged extinction by being sealed in a cave) emerging in contemporary times and trying to take over the world through television. He did this by painting himself bright pink and hosting an extremely juvenile children's show that hypnotized everyone who watched it. For some reason, the paint makes people miss the fact that this is an extremely deadly dinosaur, so Garfield has to save the day.
In "Moo Cow Mutt," Garfield decides to play a trick on Odie by convincing him that he's actually a cow, not a dog. At one point, he dons various disguises to pretend to be various passerby and call Odie a cow. His personas and outfits include a rich gentleman (a top hat and large white mustache), a little girl (a pink dress and blonde wig), and a cowboy (a Stetson hat and bandanna). Garfield fails to cover up his bright orange fur for all of these, but Odie is still fooled.
In Get Muggsy!, the title character's friends (an opossum, raccoon and spider) need only stuff sticks of white gum in their mouth to fool others into thinking that they are beavers.
In "A Charming Day Off" on Goldie & Bear, Prince Charming tries this and fails with a pair of glasses and a bad fake mustache. Goldie and Bear recognize him immediately, rightly call it a bad disguise, and insist he get a better disguise before the King's Men see him. They end up disguising him as a bush.
On Goof Troop in order to convince Pete that he doesn't need any more children, PJ disguises himself as a baby. PJ is a very overweight eleven-year-old, and besides that is Pete's son, whose apparent absence was not remotely explained until Max says he's at the store several minutes later, so Pete should have noticed (he didn't). Dramatic Irony is Played for Laughs here, with Pete delivering the lines, "Aww, kind of reminds me of PJ back when he was cute!" and "PJ was never this bad!" The former of the lines results in PJ biting Pete, with his fully developed adolescent teeth, and Pete still doesn't notice. He does, however, comment on how absurdly big he is. At least PJ's acting was better than it usually is.
In He-Man and the Masters of the Universe (1983), He-Man is basically Prince Adam with different clothes and... that's it. Same face, same haircut, same body, with a tan; his voice was deeper, but he spoke in nearly the same speech patterns.note He called the king and queen by their royal instead of parental titles. Likewise, Kringer becomes Battlecat by... putting some dark red armor on.
His sister was pretty much the same. She-Ra's only real difference from Adora was longer hair and a change of clothing that didn't hide her face at all, and seeing as Alura was an Action Girl in her own right who used to work for Hordak before her Heel–Face Turn (as a moderately high-ranking officer, no less), you got the idea that the Horde was kind of dumb.
Averted in one episode, where Kobra Khan disguises himself as a human: there is no resemblances at all, except in his speech... and Orko is still able to see through it.
In "Helga's Locket," Helga accidentally loses her precious Arnold locket—which she's just had engraved with a signed message declaring her love—and Grandpa finds it, prompting her to attempt various schemes to get it back before he and Arnold and can open it. At one point, she disguises herself in a black trenchcoat, derby, glasses, and fake mustache and calls herself "Bernard Flotsam," a rich antique art collector. This somehow manages to fool Grandpa despite several near misses, such as a pigtail poking out from beneath the hat or her voice slipping back into its normal register. When she does manage to snatch the locket and run off (only to lose it again), Grandpa, who's finally wised up, screams "AND YOU FORGOT YOUR MUSTACHE!"
The same episode has Helga hiding in a container of blank mannequin heads when she sneaks into the basement to get the locket back. Despite being the only "head" in the box with hair and facial features, Grandpa still doesn't recognize her. The poor man probably needs glasses.
In the episode "Suspended," Harold is suspended from school. When he discovers that being suspended isn't all it's cracked up to be, he repeatedly attempts to sneak back into P.S. 118. At one point, he hits upon the idea of pretending to be a pizza delivery man, and so dons what he dubs a "foolproof disguise": a fake black mustache, chef's hat, apron, and a striped shirt with his name on it. Unsurprisingly, Principal Wartz isn't fooled by the trick, even when Harold attempts a horrible Italian accent to convince him.
Hip-Hip and Hurra use them all the time. There are a few rare examples when the disguises actually work.
Alluded to in the Home Movies episode "Camp." Coach McGuirk is on the run from cultists, and among the long list of things he asks from the people he's staying with is a fake mustache. The thing is, in the time since the cultists last saw him, he's grown a full beard. In effect, he wants a "paper-thinner" disguise than the one he already has.
Happens all the time in The Houndcats, especially given the size of Puttypuss, the "cat of a thousand faces."
Hurricanes: In one episode, Napper's younger brother Nigel joined a gang of hooligans and Stavros Garkos decided to use them to convince the World Soccer Association (that series' version of FIFA) to shut down the Hispanola Hurricanes' stadium. When Nigel saw the hooligans' true colors, he agreed to spy on them. When trying to collect data from Nigel, Napper approached him wearing sunglasses and a fake mustache as a disguise to avoid being recognized by the hooligans. The only hooligan to see Napper in that disguise saw through it.
Invader Zim utilises the "brilliant" disguise of a wig and contact lenses, leaving his three-digit hands, green skin and lack of ears and nose exposed, a fact that only Dib recognises, while his robot henchman's disguise is a bright green dog suit with obvious zipper and stichings. Glimpses of other Invaders shows their disguises as equally pathetic, so it isn't just him. The trope is averted with Tak, who proves her competence by using a realistic holographic disguise.
The paper-thin disguise is in effect to the degree that at one point one of Zim's contacts falls out, which a small boy sees and begins screaming "ALIEN!". Zim promptly puts the contact back in and the boy says "Oh, never mind."
In another episode, he dismisses it as Pink Eye.
And of course when Zim gets abducted by Sizz-lor, his former boss/warden, he fails to recognize him. While at first this is somewhat justified because Sizz-lor is wearing a gas mask and body suit, when he changes back into his normal fry cook outfit, Zim still doesn't recognize him until he puts his hat on, despite his face and NAME TAG having been revealed first.
In "The Girl Who Cried Gnome" Zim's disguise is just a bear costume and when there's a news story on him later the artist's depiction has a normal human face.
Then there were the 2 mantis-like aliens from "Abducted" whose costumes consisted of aprons with human bodies printed on them and paper-mache masks on elastic strings. Even Zim isn't fooled.
Brain from Inspector Gadget is able to fool Gadget sometimes just by wearing a hat, glasses, and fake mustache and he never recognizes him no matter how bad his disguise is.
On Jimmy Two-Shoes, Jimmy managed to pass for Molotov in a spacesuit with nothing but a crudely made stuffed head on a pole.
In Johnny Bravo, one episode features a shark walking on its tail fin wearing a RichardNixon Mask at the tip of its snout. Although a scarce few are suspicious, most are fooled by the disguise.
Another episode featured a werewolf girl, who was perfectly disguised by a piece of cloth the size of a napkin over her the lower half of her face.
Johnny Test: To convince a coalition of girls to transport them back home before their parents arrive, Johnny Test disguises himself as a girl. How does he do it? By combing his hair back, putting on lipstick, and wrapping his outer jacket around his waist. The girls are doubtful at first, but he is feminine enough, and they take him, his sisters, and Dukey back to their house. When his parents come home, even his dad is surprised with his "transformation".
And don't forget Dukey. "He's a kid with a rare hair disorder, not a dog." Sometimes he accomplishes this by walking on two legs, and nothing else. He sometimes wears a t-shirt that says Not A Dog.note As a Bilingual Bonus, when the Test family goes to Paris (due to Johnny's "magic"), he wears a new shirt with "Not a Dog" written in French.
In one episode of Kaeloo, Stumpy is denied access to a girls-only nightclub by a bouncer, so he returns in a wig claiming to be a girl. This fools the bouncer despite him having seen Stumpy literally a few seconds earlier.
In Kim Possible, Shego donned a wig and a dress to pull off a Show Some Leg distraction on a guy she'd previously tried to hold for ransom. She succeeded despite doing nothing about her green skin. Even after the wig fell off, the guy still wanted to date her.
Averted with Camille Leon, except in her second appearance.
Ron does this in an episode when he wanted to go as the hero "The Fearless Ferret." Kim wasn't fooled by the disguise since she knew Ron since preschool and he didn't put in any effort into looking and acting different to fool anybody.
In the King of the Hill episode where Dale is a Bounty Hunter, when he disguises himself as a flower delivery man to attempt to gain entry into the fugitives house, he doesn't even bother taking off his "Bounty Hunter" hat. Unfortunately for Dale, this works about as well as you would expect. To be fair, he never takes hat off unless forced to, since he is self-conscious about his bald spot.
In Krypto the Superdog, Krypto's only disguise is a cape with a shield on it. And yet no one, not even the boy's parents, suspected that their dog is an alien dog.
Actually Chris's little sister Sophie figured it right away, but since she's a baby their parents didn't believe.
Hilariously subverted in League of Super Evil, where the gang are attempting to gain access to a prestigious restaurant. A man enters the lobby who is quite clearly just all four members of LOSE stuffed inside a trenchcoat and matching hat with a pair of sunglasses and a false moustache on. He is allowed through without incident, and is immediately followed by an IDENTICAL man, whom it turns out IS the gang in a trenchcoat. After the disguise has failed epicly and LOSE have been thrown out into the bins, Red Menace remarks "Maybe we should have gone in before the other guy."
Glaringly obvious in Lilo & Stitch, where everyone notices Stitch isn't a normal dog, but Jumba, a six-foot tall purple guy with four eyes and four fingered hands and his partner Pleakley, who has an exposed antenna, 1 eye, and three fingered hands are able to pass for human with human clothes, combined with glasses and a wig respectively. Nani does notice the weird shape of Pleakley's head, but assumes it became swollen after Stitch chewed on it. Jumba casually replies "Actually, [Pleakley's] just ugly".
Given the fact that within just a few episodes of the series the experiments and Jumba are running amok doing what they were intended to do, the islanders may have started accepting/adjusting to the fact that there's something weird going on and decided just not to bother.
Gantu's idea of a "disguise" is to claim he's from Samoa. Gantu is fifteen feet tall and an anthropomorphic shark. It works perfectly.
In "Llama Llama Lemonade" from Llama Llama, Mama Llama, trying to cheer up Llama about his not getting any customers for his lemonade stand, shows up to his stand wearing a brown fedora, coat and pants and bad fake mustache, speaking in an awful Australian accent and calling him "mate." The mustache falls off as she drinks the lemonade. Afterwards, just for giggles, she keeps coming back to the stand in a variety of other obvious disguises with Llama's full knowledge, including an upper-class British lady, a business suit and sunglasses and a ranch-hand.
In The Maxx, the Big Bad's sidekicks Isz, which looked like small black chess pawns, could be disguised as anything with minimal effort. Put a gray wig and purse on them, they appear as a little old lady. Hand them a bottle of cheap wine in a paper bag and they're a hobo.
In the Mickey Mouse (2013) short "Bronco Busted", Mickey, Donald, and Goofy decide to compete in a rodeo to get the money they need to repair their car. They find out that they need a horse in order to compete. After they fail to get one, they resort to having Donald pretend to be a horse by walking on all fours wearing nothing but a saddle.
In the "Christmas: Impossible" segment of Mickey's Twice Upon a Christmas, Huey, Dewey, and Louie mosey around Santa's workshop wearing their usual monochrome shirts plus green hats. Their doubts of success disappear the moment an elf addresses one as "fellow elf."
In the Mixels episode "Nixel 'Mix Over'", Major Nixel paints two Nixels, one orange and one blue, so they're the color schemes of a Flexer and a Frosticon, respectively. Even though they're no longer black and white, they're still small and cube-shaped. This doesn't stop Balk and Lunk from thinking they're "little Mixels"...nor does it stop Major Nixel from thinking they're attacking Mixels AFTER they return to base.
In an episode of the Mr. Bean animated TV series called "A Royal Makeover", all Mrs. Wicket has to do is place a fake paper crown on her head in order to convince numerous gullible London tourists that she's Queen Elizabeth II.
Done in Mr. Pickles when our "hero" successfully disguises himself as the deceased mayor of Old Town by wearing his skin and using his severed leg stumps as stilts. Nobody except Grandpa notices this, even Mr. Pickles makes no attempt to act less dog-like. At one point the Deputy Mayor notices something is wrong with her superior, but only bothers to straighten his tie.
My Life as a Teenage Robot Cluster soldier Smytus walks in to the offices of fashion giant Jean Phillip only to be shooed away by the receptionist. Smytus returns wearing a simple wig and pretending to be a Ukrainian supermodel.
On My Friends Tigger & Pooh, the Super Sleuth outfits worn by Tigger and Pooh normally wouldn't be an example, as they aren't actually trying to hide their identities. Lumpy, however, refuses to accept them as being Tigger and Pooh when they're in their outfits, even when Darby tells him that it's just them. He presumably recognizes her because her only special Super Sleuth apparel is a cap with the question mark logo of the Sleuths on it.
Fluttershy was able to avoid all her fans in "Green Isn't Your Color" just by hiding her face behind glasses and a fancy hat…and still revealing her cutie mark. Of course, once Twilight accidentally knocked the disguise away, everypony instantly recognized Fluttershy.
This actually ends up being Truth in Television, as Hulk Hogan claims in his first autobiography that he actually did this in real lifenote Minus the part about the cutie mark, obviously on a challenge from a reporter back when he was in his first run with the WWF (now WWE) as World Champion. He was challenged to prove that people would instantly recognize him on sight after telling said reporter how often he got mobbed by fans. Hogan ended up wearing a coat, hat, and glasses into a crowded street and nobody seemed to notice who he really was. The moment he took them off, however, people flocked to him within moments. While it's doubtful anyone on the show staff read Hogan's autobiography, the scariest thing about it is that if Hogan's telling the truth, this can happen in real life with actual celebrities, and obviously has, so the writers on this show may have been unintentionally lampshading this. There are more examples. Marilyn Monroe went completely unrecognized in the street at the height of her fame by not wearing make-up and adopting a less sexy walk.
In "A Bird in the Hoof", Philomena avoids Twilight and Fluttershy by wearing an obviously fake mustache. Keep in mind that Philomena looks like a plucked chicken in a town populated entirely by ponies.
It had to work. The whole bit was a Shout-Out to Benny Hill chase scenes.
Subverted in "Party Of One". Pinkie Pie compounds disguises to include Groucho glasses, a square hay bale, and a coat and hat. While this is not a strict paper thin disguise as you can not see any of Pinkie Pie, it is obviously her to the audience as she would be the only character to wear stuff like that. The disguise seems to work initially when Fluttershy sees her and runs away scared, but the trope becomes subverted when Rainbow Dash doesn't notice the disguise (or recognizing it immediately as something only Pinkie would use) as she says "Hi, Pinkie Pie" in passing.
In "Dragon Quest", Rarity disguises herself, Rainbow Dash, and Twilight Sparkle in a silly-looking dragon costume. This manages to fool the dragons, largely because there's an actual dragon among their number that is nearly identical to the costume.
In Equestria Games, Spike dons one when Twilight coaxes him to come back to the stadium, apparently forgetting he's the only bipedal creature there. A small one at that.
Inverted in Hurricane Fluttershy: Rainbow Dash sees right through Fluttershy's tree disguise before the viewer is given any other hints that it's not an actual tree.
"Brotherhooves Social" has Big Macintosh, one of the most masculine ponies in the show, disguising himself as Apple Bloom's (female) cousin Orchard Blossom by wearing a dress, high heels, and a huge wig, so he can participate in the Sisterhooves Social with her (the rules have a very loose interpretation of what qualifies as a sister, which means even a cousin or close friend can qualify). The disguise is painfully obvious (the very first line of dialogue after the disguise is revealed is "That's Big Macintosh in a dress."), and during the singing competition, his large Adam's apple is clearly visible and his voice briefly slips back into being deep and manly. At the end, the judges admit that they knew all along that Orchard Blossom was really a stallion, but due to the aforementioned rule about "sister" being loosely defined, a male pony could actually participate legally. But Big Mac still got disqualified for using his strength to destroy the obstacle course and knock away the other participants.
Humorously, there's one elderly stallion who does fall for Big Mac's disguise—he becomes smitten with Orchard Blossom and tries to woo her, only to become confused when "she" mysteriously vanishes.
Newton, of Ned's Newt, is a 6-foot tall shapeshifting blue humanoid newt. But as long as he's got some human clothes on, nobody notices. Of course, pretty much all the adults in the setting are more or less idiots.
In the Christmas special, Pooh dresses up as Santa Claus. Despite his costume only consisting of a fake white beard over his trademark red t-shirt that still exposes his round yellow tummy, it somehow manages to convince all his friends (especially Tigger).
In the second episode, Shannon disguises herself as a human to mess around with K.O. Said disguise consists of an off-kilter wig and horribly applied lipstick. Though to be fair, K.O. was only first meeting her, so he'd have no reason to be suspicious of her to begin with.
Penn Zero: Part-Time Hero In "Back to the Past of Future Balls", all characters who go back in time wear disguises to avoid being recognized by their past selves. The good guys wear fake mustaches and the bad ones wear hats and fake beards. Fortunately, the disguises turn out to be a moot point because the selves never meet.
Pet Alien: What's the most paper thin disguise ever? No disguise at all!
Phineas and Ferb: Perry the Platypus frequently employs this trope during missions to deceive his arch-nemesis Dr. Doofenshmirtz, who is completely incapable of recognizing Perry when he's not wearing his secret agent hat.
Another time, Perry disguises himself from Linda by putting on a pair of fake glasses and nose. Unsurprisingly, Dr. Doofenshmirtz is also fooled by it.
The best example has to be when he disguised himself as a plumber with a hat and a tool-belt. When he confronted Doof, this conversation followed.
Doofenshmirtz: What kind of plumber are you?
Perry: *removes hat*
Doofenshmirtz: A platypus plumber?
Perry: *puts on fedora*
Doofenshmirtz: Perry the platypus plumber?
Perry: *drops belt*
Doofenshmirtz: *gasp* PERRY THE PLATYPUS!!
In one episode, Perry gets out of Doof's trap simply by removing his hat. Doof immediately releases him, thinking he's a perfectly ordinary, innocent platypus who was put there by Perry the Platypus. Makes you wonder why Perry doesn't do that every time. Maybe he just likes a challenge.
Not to mention in the episode "Not Phineas & Ferb" Baljeet & Buford dress up as the titular duo to fool Irving's older brother Albert, with their disguises consisting of P&F's regular clothes and some very unconvincing masks (resulting in Buford having, as Irving later states "eyes in his mouth"). Ironically, Albert is the only one fooled by them.
Baljeet:(pretending to be Phineas) I know what we are doing today. Buford: And I'm British and I don't talk much.
In "Phineas and Ferb Get Busted," Candace disguises herself as TV personality Morty Williams.
Even her own parents are fooled. When they put the same Paper-Thin Disguise on a cactus, everyone thinks it's Morty Williams. When the drill sergeant shows the guards that it's just a disguise by putting it on in front of them,they think he's Morty Williams.
Pretty much any disguise Pinky and the Brain used. Keep in mind...they're lab mice. And just a few inches tall. And yet, could be mistaken for humans, with the right outfit. Brain even points this out numerous times to people, though they pass it off as Sarcastic Confession:
Taxi Driver: Hey man, not to pry but... what happened to your head? Brain: Nothing. I'm a mouse in a large mechanical suit. Taxi Driver: Oh. My fault for asking.
Sometimes he doesn't need a disguise. Once Brain got pulled over by a cop while riding a modified motorcycle. The cop just thought he was a child out for a joyride.
In every episode of the British children's animated series Poppy Cat, the badger Egbert appears in the characters' adventures as a villain wearing a paper-thin disguise. The catch, however, is that unlike most instances of this trope, the characters always recognize him who he is and even call him "Egbert," but he insists "I am not Egbert, I am such-and-such character."
Used in The Powerpuff Girls, when three adult-sized (male) crooks put on Powerpuff Girl costumes and somehow manage to deceive the entire town.
Not to mention, once they meet up, the girls themselves and each other. And the disguises were merely correctly-colored clothing and cardboard cutout masks.
The only one not fooled by the disguises was Ms. Bellum; she saw their body hair and bad manly body odor, and the fact that they kept hitting on her.
Also used when Mojo Jojo goes to the Powerpuff Girls' slumber party disguised as a little girl. Though the Powerpuff Girls (even Bubbles) aren't fooled, the other girls and the Professor are.
Or when Mojo Jojo sneaks into a show and tell of the Professor's time machine, by disguising himself as a preschool student. Which this time seems to fool everyone, including the girls and their teacher (who is one of the more responsible and competent characters).
Oddly enough, in one comic book adaptation, Mojo tried sneaking up on Fuzzy Lumpkins (usually portrayed as being about as smart as a box of hammers) disguised as one of four squirrels. Fuzzy didn't fall for it.
In the episode "Revenge of the Dark Stone" of Princess Gwenevere and the Jewel Riders, the evil Lady Kale supposedly dresses as her good twin Queen Anya to infiltrate her palace while wearing a burqa-like robe. It's a strange disguise, as Anya is never seen wearing anything like that, her eyes are still of a different color and her voice is still different too, so presumably she didn't just change her hair color in order to smuggle her two Dweasel creatures with her under the robe. Needless to say, such disguise worked perfectly.
In "Gus's Last Stand," Gus is being tormented by a nasty bully named Gelman whenever he steps onto the playground. At one point, his friends try disguising him by giving him a large gray beard and claiming he's an old man. Needless to say, the Genre Savvy Gelman doesn't fall for it.
In "Wild Child," the six main characters are each paired up with a kindergartener. As T.J. tries to find activities for him and his kid to do together, they inadvertently bother/harass/generally annoy various other people on the playground. At the end of the episode, T.J. gives his new friend his beloved hat in a Crowning Moment of Heartwarming...only to realize that he still has a bunch of angry kids after his blood when they show up to seek revenge. He's surprised when the angry group is able to spot him, as he genuinely believed that taking off his hat would render him completely unrecognizable.
In The Replacements, when the rest of the Daring family decides to tag along on Riely's first date, they do so by donning false moustaches and posing as wait staff. This includes the talking car. This doesn't fool Riely but apparently fools her boyfriend (and leads to the brilliant panicked line of "That could be anybody's talking car!").
In "Put Out to Pasture", Filbert recalls when he first met Heffer when he began a job giving away free samples at the grocery store. His boss warned him that Heffer was a master of disguise. As a result, the ever-paranoid Filbert didn't trust anyone wanting to try the free samples, and yet still kept trusting Heffer, whose disguise consisted of a paper bag with a smiley face painted on it.
In "An Elk for Heffer", Heffer manages to sneak into an elks-only club by sticking a pair of branches over his regular horns.
Heffer: I am an elk. I have antlers. Bouncer: (shrugs) You want a prize?
It gets lampshaded in the Banana Formula story when Boris worries how, after all the times Rocky and Bullwinkle have never seen through his disguises, the Law of Averages was sure to turn on him. Natasha reassures him by pointing out that Good Is Dumb.
Subverted in one episode. Bullwinkle is a star witness in the trial of a mobster, so he has to hide from the villains who want to silence him, so he and Rocky decide to get jobs at a mink farm, which they assume is the last place anyone would look for them. Unfortunately, Boris and Natasha do look there, so Rocky sticks Bullwinkle in a cage and tells him to "act like a mink". (It was all he could think of.) Well, Boris may not have been the cleverest of villains, but he wasn't that dumb; to make a long story short, the next episode started with Bullwinkle having been kidnapped.
In the Rugrats episode "Angelica's Twin", Angelica pretends to have a twin sister to get two toys instead of one. Angelica becomes "Balina" by tying her hair in a knot and rolling up her sleeves. Tommy tells Angelica to stop pretending but falls for it once she plays dumb. When Betty asks Didi if she is really going to buy two toys, Didi answers that she shouldn't stifle Angelica's creativity. The babies end up liking Balina more than Angelica.
Thoroughly subverted in "Jack And Swamp Monster". The hermit that guides Jack through various perils is very obviously Aku, Jack's arch-enemy. Jack is apparently oblivious to the fact that his new-found ally has the same color eyebrows (red), the same color skin (jet black), as well as the same voice and attitude as Aku. At one point, even the hermit's reflection in water reveals his true nature, leaving the viewer questioning Jack's sanity as he sinks deeper into Aku's trap. At the end of the episode, however, Jack reveals that he knew the truth all along, and that he's merely been playing along in order to trap Aku. The entire episode also serves to hang a lampshade on Jack's general genre-blindness; he's been tricked by Aku before in similarly transparent disguises (and, admittedly, one really good one). Then again, getting tricked by a full on shape-shifter who can change anything about his appearance isn't something to be terribly ashamed of.
It's played straight in the episode "Jack is Naked. While trying to catch a rabbit who stole his sword and gi, he dresses in a costume akin to Dorothy to keep the angry mob from catching up to him. The disguise fools everybody, until some kids rip his costume off.
Played straight with Jack again in the episode "Jack and the Rave." Jack disguised himself as one of the hypnotized dancers. While the other brainwashed dancers didn’t recognize him right away, DJ Stylbator immediately saw through Jack’s disguise and commanded the other hypnotized dancers to attack him.
Sheep in the Big City uses various poor disguises. Sheep uses them to hide from the Secret Military Organization. General Specific and his men use them to sneak toward Sheep.
Subverted in "Fear of Flying", when Homer gets banned from Moe's Tavern. Somebody who is "obviously" Homer in a bowler hat with a monocle and fake mustache walks into Moe's, speaking in an oddly stilted manner with a British accent. He protests that he's not Homer, but the innocuously named Guy Incognito, but gets beaten up and thrown out anyway. Outside, we see Homer walk past the barely conscious heap of the undisguised patron, then briefly reflect upon the implications of finding a perfect copy of himself. And then on a dog with a puffy tail.
In "Marge vs. the Monorail", Mr. Burns tries to pass himself off as "Mr. Snrub", wearing nothing unusual besides a long moustache. It does not work. It doesn't help his cause that he's accompanied by an undisguised Smithers.
In "Homer's Barbershop Quartet", Homer, Apu and Seymour are auditioning for a final member to join the quartet. One of the auditionees is "Dr. Dolittle", who is, in fact, former member Chief Wiggum wearing a moustache.
Possibly the most absurd example of all: in a parody of The Count of Monte Cristo in "Revenge Is A Dish Best Served Three Times", the Count (Homer) removes his mask, and nobody recognizes him. Then he removes his fake mole, and everyone in the room gasps in shock.
Another example of it not working is in "Who Shot Mr. Burns? Part I", when Mr. Burns dresses up in Jimbo's clothes to inform Principal Skinner his fourth-form chums and he think it would be quite corking if he were to give the school's new riches to the local energy concern. Naturally Skinner isn't fooled: "It was naive of you to assume I'd mistake this town's most prominent 104 year old man for one of my elementary school students"
In "Kamp Krusty", the villainous Mr. Black attempted to keep the campers already lowered morale steady by hiring someone to pose as Krusty. The person he hired was Barney Gumble... whose disguise involved nothing more than slapping him in Krusty's clothes (that barely even fit him, anyways), wearing a skull cap representing Krusty's head and some makeup. Most of the kids were suspicious, and Bart ends up pointing out that he's an impostor. Barney himself unwittingly confirms it simply by speaking (his drunk voice was heard instead of Krusty's voice, not to mention he called himself "Krunchy the Clown.")
In "Curse of the Flying Hellfish", Mr. Burns, Smithers, and an assassin they hired dress up as Marge, Bart, and Homer respectively in order to infiltrate the nursing home and kill Grampa. Grampa sees through the deception... because his family never visits him.
In "Hungry Hungry Homer", Duffman disguises himself in this manner as a news reporter named Joel Duffman, from The Newsly Times.
Played straight in "Homer vs. Patty and Selma" when Bart takes up ballet, and disguises himself by wearing a balaclava - in spite of his distinctive hairstyle remaining clearly visible. Everyone is fooled, and nothing much is made of how ridiculous it is.
Subverted in "The Boy Who Knew Too Much", where Bart ditched class. When he saw Homer, he quickly pushed his hair forward hoping to fool him. However, Homer has already seen Bart and was afraid the boy would figure out he ditched work. Homer's disguise was putting a hair comb under his nose as a moustache. Homer and Bart just pretended they didn't recognize each other.
In the episode "Burns' Heir," Burns shows Bart a "live broadcast" of Bart's family talking about how much they don't want him to come home. In reality, it is a group of actors Burns hired, including the Estonian Dwarf as Lisa. Bart is unconvinced until Fake Homer says his famous catchphrase "B'oh."
Amusingly enough, the actors playing the family are all wearing Latex Perfection masks; after the "B'oh" blunder, Burns excuses himself and goes to the soundstage, chewing out the actor and telling him to get it right. He shows Bart the "Simpson house" again, and Homer abruptly drops his sandwich and lets out the least convincing "D'oh!" ever...and Bart immediately buys it, sadly saying "That's them, alright..."
Also used in "Simple Simpson" where Homer becomes the Batman-esque Pie Man. At the end, Marge finally reveals that she always knew, just because it was so obviously him. Somewhat justified with the townfolks who refused to believe Homer is smart enough to create an alter ego and myths around Pie Man were created.
In "Lisa Goes Gaga", Lady Gaga disguised herself by putting on sunglasses and a grey hoodie. However, the hoodie had "GAGA" written on the back in blinking letters and it was rigged with sound effects to make it say, "Gaga Gaga Gaga."
In "At Long Last Leave" Homer and Marge try to sneak into town as Mr. Burns and Smithers. While it seems to fool Chief Wiggum, it's only because he went to get the others. He points out while dumb, he's not that dumb.
Deliberately invoked by Sideshow Bob in "Krusty Gets Busted." The Krusty disguise he dons when he robs the Kwik-E-Mart is so uncanny, that he looks like Krusty wearing only a domino mask to hide his identity (badly).
In South Park, Towelie assumes a fake moustache and a hat in order to get his "A Million Little Fibers" book published. The first person to realize this is Oprah Winfrey's sapient vagina.
Played with when Cartman disguises himself as AWESOM-O the robot. The other boys and Butters's relatives are all well-aware that he's just a kid in a cardboard costume, but everyone else is convinced that he's a genuine robot, up to and including the military.
Another episode had a male cop who went undercover as a female prostitute for sting operations. He didn't even shave off his mustache or change his voice at all and still fooled everyone.
Played for Laughs in the third Halloween episode, where one of the costumes is an incredibly well-made (and apparently fully functional) Mecha. But everyone who sees it instantly knows it's Kenny, much to his frustration.
Played for very dark laughs in "Good Times With Weapons." When the boys accidentally throw a ninja star into Butter's left eye, they put him in a crummy dog disguise meant to fool an old, half-blind veterinarian. However, when Butters wanders to a hospital, the doctor and nurse who find him are convinced that he's a real dog and send him to an animal shelter. The workers there are fooled too, to the point that they try to put him down.
In Volcano, Cartman disguises himself as Scuzzlebutt using a brown sheet, a stick, and a celery to scare his friends after they fail to find his campfire tale terrifying. He is nearly shot to death for his trouble.
After failing to get the Triangle of Zinthar from the boys, Barbra Streisand dons a fake mustache and glasses on her second attempt. The boys are fooled and freely mock Streisand in her presence, much to her indignation.
As part of his tireless quest to get Chef's dad to give him tree fiddy ($3.50), the Loch Ness Monster once disguised himself as a Girl Scout selling cookies. Chef's dad was fooled until the monster told him the price of the cookies was, of course, tree fiddy.
A subversion similar to the "Guy Incognito" example above occurs in the Spongebob Squarepants episode "No Weenies Allowed": trying to get into a tough bar, SpongeBob hits upon the idea of wearing a tough hairdo. Cut to what appears to be SpongeBob with a black pompadour out of The '50s approaching the bar. The bouncer is unimpressed and tries to unmask him... until the real SpongeBob appears wearing a rainbow wig.
Done again in "The Slumber Party". SpongeBob and Krabs must sneak into Pearl's slumber party to make sure she's not destroying the house. The scene then cuts to a girl who's obviously SpongeBob knocking on the door and trying to get into the party. Her name is "Girly Teengirl" and she just moved in from "Farawayville". Pearl quickly decides that she is Spongebob, Pearl's friends throw tomatoes at her, and she runs away, shouting, "I'm so moving back to Farawayville!" Then Krabs and SpongeBob pull up in a pizza truck, and SpongeBob sees the girl and comments on her looks. SpongeBob proceeds to play this trope straight by wearing a fake mustache; this disguise holds for a few seconds until the mustache flies away.
Played humorously straight in "Imitation Krabs." Plankton builds a robot doppelganger of Mr. Krabs that's obviously a robot, complete with monotone robot voice and exhaust pipe. It fools everyone (especially SpongeBob) except Squidward, who only went along with it because Robot Krabs gave him the day off.
Also played for laughs in "SpongeBob Meets the Strangler". The Tattletale Strangler uses only a fake mustache as a disguise (one shot even sees a receipt from the "Phony Baloney Mustache Emporium" on the ground near him) and it fools SpongeBob completely, to the point where he still buys it even after the Strangler rips off the mustache and reveals himself out of frustration.
Again played ridiculously straight in "Shellback Shenanigans", where Plankton disguised himself as Gary and not only fooled Spongebob, but also fooled the Bikini Bottom doctors!
In "Someone's in the Kitchen with Sandy", Plankton steals Sandy's pelt and uses it as a Mecha. Spongebob doesn't see anything wrong with "Sandy", even though "she" has a strange voice, holes in place of her eyes and mouth, and no air suit.
In "F.U.N.," Plankton makes off with a Krabby Patty, then ducks into a magic shop, buys a pair of Groucho glasses and a mustache, and places them on the patty itself. Spongebob, who's been pursuing Plankton, asks the strange "man" if he's seen the villain. As is the case with the Tattletale Strangler, Plankton eventually removes the disguise himself when Spongebob's inane babbling drives him crazy.
From Star Wars: The Clone Wars: Despite supposedly being the bestBounty Hunter in the galaxy after the late Jango Fett, Cad Bane's Jedi disguise is pretty pathetic. You'd think that a guy like him would put a little more effort into it.
"Around the Berry Big World" from the 2003/2007 version of Strawberry Shortcake has the Peculiar Purple Pieman of Porcupine Peak in a paper-thin disguise as a ship captain, offering to take Strawberry Shortcake and Peppermint Fizz home to Strawberryland, but actually out to sabotage them.
In the Steven Universe episode "Tiger Millionaire", Steven and Amethyst disguise themselves in order to participate in Beach City's underground wrestling ring. Steven's disguise as the eponymous Tiger Millionaire consists of slicked-back hair and a little cat nose, which somehow fools everybody. (Although Sadie does note the similarities.) Amethyst's guise is a lot more robust due to her being a shape-shifter, but she's still purple and has her gem in plain sight.
In the same episode, the Gems disguise themselves as humans... by wearing baseball uniforms and covering their Gems. It works, but only because the people they're trying to fool have no idea what humans look like, and therefore aren't too shaken by "Amy" being purple and "Sophie" being blue.
The Ruby Squad fall for one again in "Back 2 The Moon". Amethyst shapeshifts into the form of the recently defeated and bubbled Jasper. Amethyst still has her own colour scheme (which she explains away as a tan), and her gem is clearly visible on her chest. On top of that, Amethyst isn't particularly good at acting Jasper-ish, and the other Crystal Gems are only barely managing to sell that they're her "prisoners". It still fools the entire Ruby Squad.
Super Friends (1973) episode "The Androids". The villain Dr. Rebos sends a video message to the Super Friends that shows his real face. A short time later, he talks to both Batman and Superman at close range, with his only disguise being a small server's cap, and both of them completely fail to recognize him.
In one episode of Sushi Pack, Ben needs to talk to the Pack while they're in the middle of a mission, so he dons a disguise to keep their connection a secret. His disguise? A moustache that's not even the same color as his hair. That's it. He didn't even bother taking off the apron from the shop he owns.
In a Sylvester the Cat and Tweety Bird cartoon, Sylvester attempts to disguise himself as an organ-grinder's monkey in order to infiltrate Tweety's apartment. Initially it seems as though his disguise was actually working, but then he lifts his hat up and Granny whacks him in the head, with her also saying "Did you really think I would be fooled by that disguise?", making this a subversion similar to the Mr. Burns example.
Umi Car's Tiger Disguise and Bot's Poodle Disguise from Team Umizoomi
And it works!
In The Teddy Bears Picnic, two teddy bears are trying to sneak a human girl into the picnic, since she's trying to find her particular teddy bear. The disguise they put together for her consists of a pair of earmuffs, a clown nose, and a line drawn on her face. It manages to fool everyone else at the picnic until she sneezes the earmuffs and nose off.
The Turtles could fool anyone by wearing a trenchcoat and fedora, despite their green skin being clearly visible. As soon as they lost the hats, though, it was obvious to all. They did occasionally wear human masks, though.
Lampshaded in one episode of Teenage Mutant Ninja Turtles (1987) where April gave them the masks, telling them Channel 6's prop department made them. When the heroes try them on:
Michelangelo: Well, we don't look like mutant turtles anymore.
It wasn't just the turtles. Shredder, Rocksteady, and Bebop could also easily fool anyone, including our heroes. In one episode, April can't see past Shredder's disguise despite it simply being a train conductor's outfit worn over his metal costume... and yet, she found out Bebop and Rocksteady hiding behind a sheet only by catching sight of their shoes.
This is played with in one episode of the 1987 show, where Casey helps the Turtles infiltrate the Octopus Ink company. He wears a suit and tie to an interview, but still has his hockey mask and bag full of weapons. However, he's still hired quickly, not because his disguise is bad, but because the interviewer is looking for types like him. (And after getting into a violent altercation with a filing clerk, he's promoted.)
Although this was completely averted in Turtles Forever, where the 80's Turtles never make any attempt to disguise themselves whatsoever; much to the chagrin of their 2k3 counterparts. This leads to a scene where the '80s Turtles (while in the 2k3 world) proceed to casually walk the streets in broad daylight, go to a pizzeria and order pizza. Predictably every person who sees them runs away in terror and yet the '80s Turtles have no idea why. This scene and most of the 80's Turtles' depiction in the film can be chalked up to Flanderization.
"You Look Familiar", says Jinx to Cyborg in Teen Titans. Could the young villainess only see past her nemesis' cunning disguise as himself (without cybernetics), she'd undoubtedly fry his wirings on the spot and spare herself a broken heart.
In the episode "Danger" of The Telebugs, the Telebugs attempt to infiltrate the Angel Palace disguised as children. Said disguises consist of wigs and hats. Naturally, Reality Ensues when Bullybyte is immediately suspicious.
The Big Bad Wolf in Disney's Three Little Pigs cartoons is fond of this trope. He often even doesn't mind going into drag to catch the pigs. Generally, the first two pigs are often fooled by his disguises, but strangely in the original short, they AREN'T fooled by the Wolf's attempt at a lamb disguise (crouched in a basket, draped in an old sheepskin and holding an old-fashioned baby bottle.)
Pigs: Not by the hair on our chinny chin chin, you can't fool us with that old sheepskin!
In the 3-2-1 Penguins! episode, "Practical Hoax", Cavitus' and his minions' disguises consist only of Groucho Marx glasses.
On ToddWorld, this played with in "Super Sophie." Todd creates a superhero outfit for Sophie that is a reasonable disguise - most notably covering up her hair-stalks that she uses to fly that are her most recognizable feature and an obvious dead giveaway. Despite this, her general appearance is still enough that everyone, especially Stella, eventually pieces it together, especially since the voice she uses really isn't all that dissimilar from her normal voice.
In the Van Beuren StudiosTom and Jerry short "Plane Dumb", Tom and Jerry disguise themselves in blackface makeup (while impersonating Amos N Andy at the same time) when they travel to Africa. The natives aren't fooled.
The Tom and Jerry short "Puttin' on the Dog'' has Tom disguising himself as a dog to infiltrate a dog pound that Jerry is hiding in, with nothing but a yellow dog mask. The short's gags revolve around Tom trying to keep track of his mask. At one point, Jerry hands a suspicious Spike this message: "Yes stupid, it's a cat."
And he had it clearly written on a name badge just in case there was a slight chance no one would figure it out.
There's a very slight justification in that this is Tim Scam's first run-in with the girls who had never heard of him. Also the file on him they check has no picture so they don't learn what he looks like until it's too late.
In "Passion Patties," the spies are sent to investigate why people are getting strangely hooked on the titular cookies, which are being sold by a local Girl Scout Expy. Jerry thus decides to send them in as scouts themselves...despite them being fully grown teenagers. The head of their troop is slightly suspicious, but eventually lets it go.
In another episode, the villainous Dr. Gelee returns to kidnap his nemesis Clover—a short-haired blonde with blue eyes, pinkish skin, and a smooth voice—during a ski trip. By some amazing coincidence, the school's Alpha Bitch Mandy—a girl with long black hair, purple eyes, pale skin, and a grating voice—just so happens to have a new winter outfit that's identical to Clover's red spy jumpsuit. Naturally, Dr. Gelee grabs Mandy instead of Clover, just because she was wearing the red outfit. This might lead viewers to believe that the girls would be immune from any villain ever recognizing them if they didn't wear their spy gear.
In the third episode of Transformers: Generation 1, the Autobots decide to set up an ambush for the Decepticons. Hound uses his holographic projector to make a fake "rocket base" and the Autobots will be in it, under disguise, to attack the Decepticons when they show up to raid the base. What disguise do the Autobots go for? If you guessed "Disguised in their car mode in the base parking lot", congratulations, you're smarter than an Autobot. They decide to don labcoats and pass for the human scientists. Despite the fact that even the smallest of them is twice as tall as a human and about 3 times as wide.
Almost used in Transformers Cybertron. After Bud describes conventions and cosplay to the Autobots, Jetfire jokingly suggests that they pretend they're fanboys in public, to the amusement of all. However, Optimus Prime takes him seriously and thinks this is a wonderful idea until the humans talk him out of it.
And then there was Transformers Armada, when the kids dressed up the Space Team in lumpy sweaters, scarves, and goggles to take them on the bus. And it worked.
Punch/Counterpunch, full stop. His Autobot counterpart is reeeal nearby... Only exacerbated by the fact that his "second robot mode" basically consisted of turning around, lowering his shoulders, and pulling up a visor.
While the show's tagline may be "Robots in Disguise," not a whole lot of alt modes actually make for convincing disguises. Even disregarding spacecraft like Cyclonus or Cosmos or the recurring giant robot dinosaurs, plenty of characters have altmodes with the wrong colors (Scavenger, the world's only green-and-purple excavator), altmodes that don't make sense in most environments (Mirage, the F1 racer), or alt-modes that are even more conspicuous than their robot modes (Trypticon, an entire city). The live-action films, with their heavy product placement, regularly have six or seven brightly-colored and expensive concept cars driving down the road in a line without raising an eyebrow. The comic series Escalation mocked this hard.
Russian commander: “We appear to have an American F-22 Raptor, being shot at by some kind of rally vehicle. And a police patrol car, also American... under attack from a space shuttle?”
Underdog arguably does a better job than many on this list, for the way he changes his tone of voice, loses his rhyme, and generally attempts a different persona. But he does nothing to change or hide his face. And from what we see, anthropomorphic dogs are very much in the minority in his hometown.
Actually, in one cartoon, Riff-Raff comes very close to figuring it out after deciding to follow Underdog home to steal a painting he's looking after, only to find Shoeshine Boy with it; unfortunately for the villain, Underdog fool him by changing in and out of his costume again and again while moving at super-speed (to make it look like both his identities are in the same building) and Riff-Raff is dumb enough to fall for it.)
And one point during the movie, a man noticed Shoeshine sitting on the stairs and remarked on how much he looked like Underdog.
This was subverted in the VeggieTales episode "King George And The Ducky", where Jimmy and Jerry are disguised as Bob and Larry in an attempt to host the show themselves. Of course, the viewers all knew that they were not the real Bob and Larry. Then, Bob and Larry show up and are able to recognize Jimmy and Jerry in their costumes.
In The Venture Bros., the original Dr. Venture infiltrates a Super Villain Team-Up dedicated to killing him (who have also kidnapped his son) by pretending to be a Japanese super villain (from the village of Japaninawa). This is done by wearing a wig, fake mustache, a fake nipple on his chin and by pulling his eyes with his fingers so they appear slanted. He makes no attempt to hide his voice or even employ a fake accent. And his cover name, "Dr. Fandragon", is clearly composed of the only two Asian things he could think of. The weaknesses of his costume are all lampshaded by the head villain, who seems to get that 'Dr. Fandragon' isn't really Asian but not that he's Dr. Venture specifically.
Scaramantula: As do we all, my thoroughly Japanese friend who is easily, easily 6'2". Scaramantula: What is that my uncharacteristically hirsute Asian comrade?
Also, Hank's disguise as "Russian Guyovitch", a fake goatee and an outdated Monarch minion costume. Both Sgt. Hatred and Brock are fooled.
The superhero team The Super Gang all make fairly serviceable attempts at Clark Kenting (with the exception of Ghost Robot, who, being a Tin-Can Robot, would have a difficult time being inconspicuous no matter what), but what pushes them into this is that their secret identities happen to be the entire Action 5 News Team. So a news team consisting of two burly white guys, a short black guy, a skinny woman, and a robot do news reports on a superhero team consisting of two burly white guys, a short black guy, a skinny woman, and a robot. Add in some Steven Ulysses Perhero names, and you have this trope.
Played for laughs in the Wallace & Gromit short film "The Wrong Trousers". There, a villainous penguin dons a disguise, which consists solely of a rubber-glove wig, for his crimes. No one sees through this fiendishly clever ruse, as they all think he is a chicken.
In "Castle Caper" on Wallykazam!, Wally uses one when posing as a "cake delivery guy" to smuggle his dragon Norville into a castle taken over by Bobgoblin as a Trojan Horse. The ploy fails, though whether or not the paper thin disguise was a contributing factor is debatable.
In Walter Melon, Melon is a hero for hire who replaces heroes temporarily when they're somehow incapacitated. Despite Melon being an obese bald man with a huge nose, no one can tell the difference.
The Whatever Happened to... Robot Jones? episode "School Newspaper" had Principal Madman try to get back at Robot Jones for taking embarrassing photographs of him for the school newspaper by turning the public against him, which he did by photographing himself doing bad things disguised as Robot. Madman's Robot Jones disguise consisted of a cheap mask and a gray bodysuit, yet everyone at Polyneux Middle School is deceived in spite of Madman being an obese adult and his bodysuit lacking such details as Robot's "clothes".
Carl the Evil Cockroach Wizard from Yin Yang Yo!lives for this trope. On at least one occasion, he actually used it when there was absolutely no reason to. When his brother Herman lampshaded this, he nonchalantly responded "I love to play dress-up." Taking the tone of the show into consideration, there might be some Parental Bonus in that. Yin and Yang are not so good at disguises anyway. One episode Yang put on a mustache and tried to trick Carl. He did fall for that and said "Here, you dropped your mustache... Ah, it's one of my enemies wearing a cheesy disguise!".
When in his civilian identity, Robin in Young Justice needs to be in disguise (apparently it's something Batman insists on). All he does is pull on a pair of sunglasses. Then again, the team does not have any contact with Dick Grayson unless Artemis goes to Gotham Academy.
A better example of this trope would be Conner. He doesn't wear a mask or any costume at all, but so long as he isn't wearing a Superman t-shirt, no one recognizes him to be Superboy.
Its even worse than that; Connor refuses to wear anything but black super-man T-shirts, even in his civilian identity. Presumably the only reason why his classmates haven't worked it out yet is that he's part of a covert OP team that doesn't get a lot of media attention.