A character that the other characters should recognize (or at least recognize as out of place) dons a disguise and is treated as neither recognizable nor conspicuous. This disguise is so completely transparent that the audience wants to shout "For the love of God, it's him!"
The external reason for the flimsy disguise may be that the creators want to signal the presence of a disguise to the audience before the other characters catch on (a sort of Reverse Whodunnit). Sometimes, the character may also be a Special Guest the director wants to get their money out of. All the same, you often get The Reveal staged in such a way to make it clear that the director really thought you wouldn't have worked it out by now. For the more perceptive viewers, it's a case of The Untwist.
While this is not quite a Discredited Trope, these days Paper Thin Disguises are parodied as often as they are used seriously. The trope is still an important dramatic convention in live theater and opera productions — where a really good disguise would render the character unidentifiable from the cheap sets, and be beyond the scope of the prop budget to boot — but is usually employed along with some kind of nod to audience acknowledging the absurdity. This can sometimes be exaggerated for comedic effect, for example wearing bunny ears and becoming indistinguishable from a real rabbit, or pretending to be an ancient statue by simply standing still in a specific pose. Children's shows still employ this trope regularly without any parody element.
This trope differs from the general case of Wig, Dress, Accent in that a Wig, Dress, Accent disguise is always plausible. Paper Thin Disguise also includes the element of being staged as if the disguise really is convincing, which is not generally present in Wig, Dress, Accent.
Also see Conspicuous Trenchcoat, Not a Zombie, Newspaper Thin Disguise, Clark Kenting, Mr. Smith, Hugh Mann, Holding Both Sides of the Conversation, Charlie Brown from Outta Town, and Most Definitely Not a Villain. Contrast with Full Body Disguise and Latex Perfection.
The Trix rabbit has tried about a million of these. Subverted in that they never work for more than a few seconds, and the few that do work are foiled by the Rabbit's undeniable addiction to the cereal.
One good disguise the Trix Rabbit once used was to somehow turn himself into a cute, adorable bunny (they used a real rabbit in the commercial) and changed tactics, not talking at all and simply trying to sneak up on the kids. Unfortunately, his addiction to it gave him away as it always did.
This 1972 commercial was one of the first to show Barney pulling this stunt. In this case the ONLY change was putting a fake beard on. And he still managed to fool Fred.
An ad for cheap cell phone service featured a woman who was saving money for her expensive cell plan by having her son travel free on a plane trip. She'd dressed him in a floppy-eared Halloween costume and stuffed him inside a pet carrier; hearing them converse, a baggage handler marvels at the "talking dog".
The dog from the Bush's Baked Beans commercials once appeared in a labcoat and false mustache, posing as a food science researcher. For those who haven't seen these ads, be aware that the dog is a real golden retriever, not a cartoon mascot. He's also shown up as a Bedsheet Ghost of the recipe owner's grandfather, but is revealed when the man explains, "Grandpa didn't have a tail."
Seen in a TV ad for Speedway, featuring a contest for their Speedy Rewards card loyalty card. A man keeps coming in and using his card, wearing a series of ridiculous disguises. Finally, the clerk, who isn't fooled for a minute, tells the customer that he can use the same card as many times as he wants and still be entered in the contest each time. MST3K Mantra, since if you think about it for more than a few seconds, you realize that no matter how well he disguises himself, the card always carries the same computerized details about his identification. (Then again, he might not be smart enough to realize that.)
A Dunkin' Donuts ad had the company donut maker (a portly little guy with a moustache) spying at a rival donut place dressed as a woman, coyly holding a hand over his moustache and not fooling the anxious counter man.
In one McDonald's commercial from the '70s, Ronald dresses up as a mailman to thwart an attempt by Grimace (who was evil at this time) to steal some milkshakes. The disguise is little more than a hat.
One of the Naked Gun-type ads for Red Rock Cider has the Comedic Hero working undercover in an ice cream van called "Mr Policey" and labelled UNMARKED POLICE CAR. This naturally leads to a Visual Pun where a customer asks for a couple of cones and gets two traffic cones instead.
Frank Drebin: A hot tip led Sgt. Doughray and me to Ascot. We mingled unobtrusively for a while before dividing forces. (Doughray and Drebin are wearing dark men's suits and fancy ladies' hats.)
In the one-shot Hiding in Plain SightHarry Potter gets Lasik eye surgery and becomes completely unrecognizable to the pureblood wizards at Hogwarts without his trademark glasses. Then the Aurors try to recreate 21 Jump Street at Hogwarts. The muggleborns have absolutely no trouble recognizing the incredibly out-of-place "first-year students".
A large degree of Kirby fanfiction gives Kirby the ability to become completely indistinguishable from whoever he's taken the power/costume of, despite the obvious size differences.
In the Calvin At Camp episode "The New Kid," Larry Koopa infiltrates the camp while wearing nothing but a Mickey Mouse hat.
In Nobody Dies, in order to pacify a rampaging A.I. based on Fallout 3, Gendo tricks it into thinking he's Abraham Lincoln simply by wearing a top hat. It probably helped that he already had the beard.
Hivefled: in one of the less grimdark scenes, the four trolls with the smallest and thus most easily-concealed horns dress up as humans to go food shopping. Not only are they wearing hats and gloves in June and concealing their grey skin only with face-paint, but John only just manages to stop them talking about eating babies in public.
Zigzagged throughout Like One Sundered Star, where superhero identities are Paper Thin Disguises when they have any efficacy at all. Karkat and John are the only ones who DON'T immediately ID each other as Heir and Hemogoblin out of costume. Dave and Bro barely even give lip service to the trope, removing their shades while "on duty" but making no other effort to conceal their faces. Kanaya has to drastically redesign Rose's Seer of Light costume into a real disguise after her Superpowered Evil Side rampages through New York unmasked.
In Welcome To The FamilyLight Yagami determines that not even the genii of Wammy's House can withstand the mighty stealth powers of the "magic hoodie" that somehow renders him unrecognizable whenever he goes out to do nefarious things.
"Judy in Disguise (With Glasses)" is a hit song for the Louisiana-based John Fred and His Playboy Band in early 1968. The song was a parody of The Beatles' hit, "Lucy in the Sky with Diamonds".
The members of Pink Floyd would sometimes mingle with the audience for drinks during the intermissions for their shows, with no disguise other than leaving their instruments behind. They were almost never identified as the people who had previously been performing under a spotlight right in front of them. Of course, all four of them were pretty unremarkable-looking and they tended to stay out of the public eye, but still...
Happens a few times in The Far Side. The most notable example is a polar bear with a penguin mask that doesn't even cover his whole face. And yet the penguins wonder why their numbers are diminishing.
Subverted when Calvin assumes (probably from seeing too many TV shows where this trope is in effect) that he'll be unrecognizable in his "Stupendous Man" costume, and is thoroughly confused and frustrated when it fools nobody. Especially funny is that his mom, one of the people he expects will be fooled, made the costume for him in the first place.
Calvin attempts to do this trope with Hobbes (wearing a trenchcoat with Hobbes on top) in order to sneak into an X-rated movie. Going by the ticket seller's remark in the final panel ("This is a new one."), she evidently did not fall for it.
Calvin once donned a fake nose, glasses and mustache and when Mom came to ask him about a broken lamp, he altered his voice and asked, "Who ees thees Kahlveen?"
Prickly City: How to disguise a coyote as the Lost Bunny of the Apocalypse: bunny ears.
Andrι the Giant: In the spring of 1986 (following his WrestleMania 2 battle royal victory), Andre requested time off to go on a tour of Japan, heal from legitimate injuries, and begin filming scenes from a movie he was hired to star in, The Princess Bride. At the time, he was engaged in a 3-year-old feud with Big John Studd over whom was the true giant of wrestling, and a storyline was contrived to have Andre "miss" several high-profile tag-team matches (with a partner of his choice) against Studd and King Kong Bundy. Eventually, at Bobby Heenan's behest, WWF president Jack Tunney "suspended" Andre. Later in the summer of 1986, a masked wrestler, identifying himself as the "Giant Machine" appeared, targeting along with other masked "Machine" wrestlers Studd and Bundy. The villains insisted that the Giant Machine was in fact Andre. They were right, except they were unable to mask Andre to prove his true identity (much to the delight of fans), and the WWF's lead announcers, usually Vince McMahon, Gorilla Monsoon, or Bruno Sammartino, speculated that the "Giant Machine" might be one of several famous Japanese wrestlers.
Indeed, Bundy and Studd never were able to prove their case to the fans, which had they succeeded Andre would have been "fired" (for circumventing Tunney's suspension). However, the storyline was always left open so that if Andre's health forced his retirement, the "Giant Machine" would have been unmasked. However, Andre's health held up enough and after finishing filming of The Princess Bride and concluding his Japanese tour he was "reinstated" ... and a heel turn later that led to his famous WrestleMania III match with Hulk Hogan etched his name in history.
At the height of the Bundy/Studd-Machines feud, Heenan introduced his own stable of "masked" wrestlers during a segment of "The Flower Shop." It was obviously Studd and Bundy wearing paper masks, and they quickly revealed themselves to scornfully mock Andre.
Delirious tried to do CM Punk's steal an audience member's clothing and hide in the crowd trick but his mask and the tassels hanging off of it stuck out like a sore thumb. Daizee Haze has also worn some disguises in her efforts to aid Delirious...with mixed results.
Pip Bin of Bleak Expectations is always fooled by his nemesis Mr Gently Benevolent's disguises, though they're always comically thin and he's prone to slipping back into his accent, saying his evil internal monologue out loud.
Pip: Mr Benevolent! How did you fool me for so long? Mr Benevolent: Do you know, I genuinely have no idea.
The late Linda Smith had a routine complaining about the use of this trope in opera: "Someone puts on a big hat and suddenly no-one can recognize them, even people who they've been talking to for half an hour. If that worked in real life, the witness protection program would consist of a selection of headgear."
It's not unusual for disguises to seem paper-thin on stage, a dramatic convention to make allowance for limited props and budget. Willing Suspension of Disbelief is encouraged in this scenario.
In Ken Ludwig's Lend Me a Tenor, the theater manager's assistant Max disguises himself as the visiting tenor Tito Merelli after Tito is found dead in his hotel room. This works on the opera's audience, as they have never seen the real Tito and won't know the difference. However, Tito's Not Quite Dead, and is running around Cleveland in the same costume Max is wearing (Tito brought two identical costumes). Saunders, the manager, runs into Tito several times without realizing the costumed tenor is not Max, despite Max and Tito, even in costume, looking nothing alike.
In many stagings of As You Like It, Rosalind's "Ganymede" disguise is portrayed as this. In these versions, Orlando recognizes her at once, she realizes as much, and their subsequent "tutoring" scenes together become coy, humorous flirtations between the pair, who through role-playing can be frank with each other in ways a young couple of the time ordinarily couldn't.
In Holy Musical B@man!, Alfred is fired by Bruce, later returning as "O'Malley the Irish Butler" who is just Alfred wearing a hat and a ginger beard.
In Jimmy Neutron's Nicktoon Blast, when Ooblar is breaking into Jimmy's lab, he dons a disguise that consists of: Groucho glasses, a camera, and a Universal hat. Jimmy sees right through it, but apparently no one else did.
This was the main gimmick for the Purr-Tenders toy line: fluffy plush cats wearing fake ears and muzzles so they could pass as 'exotic' animals like dogs and mice. (The fact that they could all communicate with humans and came in pink and purple apparently didn't make them exotic enough.) Somehow, the disguises worked... until they started purring.
In Apollo Justice: Ace Attorney, Apollo never notices the uncanny resemblance between the picture on the wall at the Wright and Co Offices and the victim of his first case (not even noting familiarity) even when the only difference is a goatee. On the other hand, Phoenix notices from the first meeting. The player, on the other hand, stands a chance of noticing at first glance, even without color.
Furio Tigre disguises himself as Phoenix Wright in order to frame someone for murder. This 'disguise' consists of a suit, a fake attorney's badge (made of cardboard!) and loudly proclaiming himself to be Phoenix Wright. It works despite every major player in the case knowing Phoenix personally. Because they have the same hairstyle. ... Furio Tigre is huge and orange. Gumshoe mentions that many people on the court had "big question marks on their heads" when Not Phoenix made his apparition, but every time someone tried to point this out, Furio literally roared them into silence. Even more bizarrely, the disguise is apparently good enough to fool the player — the first you see of Furio Tigre is in the chapter intro where Phoenix Wright loses a case... and he's rendered as completely indistinguishable from the real Phoenix.
Trials and Tribulations subverts this with Dahlia Hawthorne when she appears to turn up in "Bridge to the Turnabout" with a different hair colour and nun's garments (retaining the same hairstyle and mannerisms, thus the Paper-Thin Disguise). The subversion? It's actually her twin sister.
Trials and Tribulations, the one difference between Godot and Diego Armando is basically a pallet swap and a face visor.
Chris in Princess Waltz. How obvious is it? Before The Reveal, knowing how bad a job she's doing acting, Chris asks in a roundabout way if Arata is sure he doesn't suspect her of anything. And barely refrains from mentioning what: Being a girl. It gets worse. He walks in on her with no disguise (bath) and still doesn't get it. All the yaoi fangirls in the class squee...
Little Busters! has Mask the Saito, a mysterious masked man that appears and starts challenging people if, after being returned to the bottom of the battle rankings early on, you can make you way up to the top again. At first glance, it isn't obvious who it is, but as soon as he starts talking it's very clearly Kyousuke's voice. If you lose to him, he doesn't even bother to keep up the charade, turning around and walking off (revealing distinctive red/brown hair) while throwing the mask away. Riki is faintly bemused by the entire thing, but plays along.
Katawa Shoujo parodies this to demonstrate just how detached from reality Kenji really is. During one of their encounters, Kenji mentions that he's going to the store and Hisao, well acquainted with his paranoia at this point, sarcastically asks if it's safe for him to go outside. Kenji, immune to sarcasm, counters that he's safely disguised because he has a hat. (Bonus points: he's not even wearing a hat.)