Paper-Thin Disguise/Film

"Mr. Furious: That's because Lance Hunt is Captain Amazing. Blue Raja: Oh here we go... Shoveler: Oh, don't start that again! Lance Hunt wears glasses. Captain Amazing doesn't wear glasses. Mr. Furious: He takes them off when he transforms. Shoveler: That doesn't make any sense. He wouldn't be able to see!"

- Mystery Men

Examples of in  include:

Animated
"Clone: Clearly you are defective beyond repair. Guards, take them to the incinerator! (All cower in fear) Clone: Well? What are you waiting for? You two (motions to Bob and Dr. Cockroach), take them away. Dr. Cockroach: Seriously? Clone: Yes. And here's a security pass in case you run into any trouble. Would you like a gun?"
 * Both subverted and invoked for laughs in Monsters vs. Aliens: The monsters try to rescue Susan from an alien ship by dressing as clones of the evil alien overlord. The disguise consists entirely of a vest, with the evil alien overlord being a purple tentacled creature, and looking nothing like the monsters. Link stops the clone escorting Susan, saying that he, Galaxar, demands the prisoner be released, leading to this:


 * In Disney's The Jungle Book, Baloo the Bear impersonates a primate by putting some leaves on his head and two large coconut quarters on his lips.
 * And just before that, Bagheera has successfully passed himself off as part of the ancient ruins by assuming the same pose as a row of jaguar statues, even though he's nearly solid black and the statues are all a light shade of gray.
 * Mulan: All Mulan has to do to pass for a man is put on some men's clothing and put her hair up. As The Nostalgia Chick wisely said when Mulan's cover was blown: "Just put your hair back up, it's like the gender equivalent of Clark Kent's glasses."
 * Megamind has a standard yet humourous approach to this with the minion-fish in his great big metal body - where he becomes the new hero's "space step-mom" by putting on an apron and a wig.
 * In Team America: World Police the gang has Gary disguise himself as a terrorist; he goes through a montage of what seems like extensive plastic surgery only to reveal that they just painted his face brown and glued some hair to his face.
 * Played with in Robin Hood. Prince John figures out Robin's disguise as a stork (though the stork costume was convincing), while the Sheriff claimed he could see through any disguise Robin could cook up (he doesn't). Earlier, Prince John and his guards failed to see through Robin and Little John's gypsy costumes, though it did make John more perceptive to catch on to Robin the second time around. Hilariously, none of the bad guys see through Robin's blind beggar disguise, though Trigger suspected something.
 * Aladdin: Just a change of clothes is all it takes for people to not recognize Aladdin as Prince Ali. One would think that Jasmine, who spent quite some time with the street rat, would have noticed that the boy she met in the market was the same as this guy. It isn't until he asks if she trusts him, just like earlier, does she suspect something.
 * In Home on the Range cattle rustler Alameda Slim works with henchmen so moronic that no matter how many times he demonstrates before their eyes that he can put on the hat and the glasses and it's still him, they react with shock that a stranger has suddenly appeared before them... every. single. time.

Live-Action

 * King Henry V in Kenneth Branagh's film of William Shakespeare's play Henry V. King Henry dresses himself as an archer and visits his troops during the night before the battle of Agincourt, using a pretty transparent name "Harry Leroy". Harry is, of course, colloquial from Henry, and while Leroy is a Welsh name, it is also French for le Roi, "king". When one of the archers asks him if he is of Welsh origin, he answers affirmatively; before he became king of England, he was Prince of Wales.
 * Lampshaded in Mystery Men, when the city's resident superhero appeared as his mundane counterpart. There was an argument between two of the titular Mystery Men at one point, in which The Shoveler insisted that they couldn't be the same person because the regular guy wore glasses - and the superhero didn't. "He wouldn't be able to see!"
 * The Princess Bride: Despite being his true love, Buttercup can't figure out who the Dread Pirate Roberts is based on the fact that he wears a Zorro mask and hair wrap. She's also blindfolded when they first meet and has plenty of time to listen to his voice before looking at him.
 * In the (extremely loose) film adaptation of The Dark Is Rising, the Black Rider spends most of the film disguised as an extremely goofy country doctor with huge glasses and a tweed suit.
 * In A Hard Days Night, all it takes for Super Famous Beatle Ringo Starr to slip into anonymity as he wanders around London is a cloth cap and an overcoat. The disguise even lasts when he loses the overcoat, so the cloth cap must have special powers. Reaches heights of absurdity when, having been arrested, Ringo insists to the policemen that he's Ringo Starr, but they refuse to believe him - because he's wearing the cloth cap.
 * A couple of fangirls see through the disguise at one point, forcing Ringo to make a hasty retreat.
 * Also Paul McCartney's fake beard in the opening number.
 * Similarly in Help!, the Beatles go to the airport in fake beards and mustaches to avoid being noticed by Cult members.
 * To be fair, in Help! those were much more elaborate costumes. John even went so far as to stay in a wheelchair to avoid recognition, far from simply wearing a cloth cap.
 * In Enchanted, Nathaniel goes unnoticed in a restaurant kitchen because he is wearing a chef's hat as his only disguise element.
 * Done in the old WWII propaganda film Beasts Trom The East. The Japanese soldiers are disguised as trees throughout, even when moving or shooting.
 * Stanley Kubrick's Lolita features Peter Sellers in not one but two disguises.
 * This trope was quite commonplace in the short films of The Three Stooges. In one, the boys end up cooking/catering at a party for a judge who wants to send them up the river. Moe: "Oh, he'll never recognize us in these outfits!" (Apparently, just wearing a white jacket and chef's hat renders you totally unrecognizable.) In another Western-themed short, Curly masquerades as a Justice of the Peace, but is not recognized by Christine McIntyre until he lifts the tiny (and I mean tiny) little toupee off his head, points at his face, and mugs.
 * Batman: The Movie, based on the Adam West 1960's Batman TV show.
 * Alfred's "disguise" was to cover the top half of his face with a black cloth with eye-holes, (like 50's Disney Zorro). He was still wearing his suit and put his glasses on over the mask.
 * On the other flipper, when The Penguin tries a more elaborate getup, the Dynamic Duo aren't fooled one bit..
 * In the Live Action Adaptation of Cutey Honey, the title character had several costumes/disguises, but she invariably had bright red hair. Imagine it; you're in a Tokyo train station full of girls with black hair, and you're trying to find Cutey Honey. How long would it take you to spot the redhead?
 * In Velvet Goldmine blue-haired rock star Brian Slade turns up to a concert in a "disguise" consisting of a large hat and coat. Although his ex-wife reveals that she recognised him, and public opinion towards him had already soured somewhat, it seems a bit odd that no one bats an eyelid at his appearance, given that he is still very famous, and very poorly disguised.
 * In What's Up Doc? one of the characters attempts to disguise himself by wearing a fake mustache. Not only that, but it's upside-down. The main characters seem to realize who he is, though.
 * Two female soccer players in Shaolin Soccer disguise themselves as men by sporting a fake mustache and goatee and talking in a deeper voice.
 * In Friday the 13 th Part 2, Ginny convinces Jason she's his mother by simply putting on Pamela's sweater and acting like her. Jason eventually does see through the ruse, but only after spotting his real mother's severed head.
 * In The Legend of Zorro, Zorro's son is unable to recognize his own father's face or voice, while talking to him, because part of Zorro's eyes are covered by his facemask.
 * Parodied in Hot Shots: Part Deux in a Shout-Out to the film The Guns of Navarone. When intercepted by an Iraqi patrol boat, the heroes pretend (poorly) to be local fishermen. Ramada's disguise consists of a very fake looking mustache. The soldiers don't notice anything amiss until they see her enter the ladies' room.
 * The Rocky Horror Picture Show: Dr. Frank. N. Furter fools both Brad and Janet with his paper thin disguises, first as Brad to seduce Janet and then the other way around, and all he's wearing for a disguise are glasses and a wig for Brad and a wig for Janet. Then again, it's dark in both of their rooms and he seems to be able to imitate their voices perfectly.
 * In the Star Wars Prequel Trilogy, Palpatine doesn't do much more than wear dark robes and speak in a raspier voice to disguise his identity, in spite of being a public figure.
 * Played straight and averted in The Major and the Minor, where Ginger Rogers' character dresses like a little girl to take a train for half price. The Major falls for it, as do the cadets at his school, but most other people realize that she can't possibly be under twelve, with an actual teenage girl pointing out her distinctly adult features and the fact that she's acting more like she's six than eleven.
 * In Heroic Trio, Anita Mui's character wears a small mask that molds to her face so much that it shouldn't really fool her husband. Judge for yourself here and here.
 * Played with in the first of The Green Hornet movie serials. One episode has the gangsters trying to steal an election, and they use the classic "wear disguise and vote multiple times" method. Some of the reporters watching the polls see through the rudimentary disguises. However, it's not clear if the disguises were paper-thin to make things easier for the audience or an attempt by the gangsters to give the poll workers Plausible Deniability—the gangsters used bribes other times ....
 * Played with in Green Lantern. Hal Jordan's Domino Mask is supposed to protect his identity. After saving Carol Ferris' life, Hal appears at her window in his Green Lantern persona in an attempt to "get the girl". Carol almost immediately sees through his disguise, pointing out that she had known him all her life and she wasn't dumb enough to not recognize him because she couldn't see his cheekbones.
 * The 'men' at the stoning in Monty Python's Life of Brian are all women with fake beards. They keep forgetting to speak in a lower voice and refer to each other as "she" before catching themselves. Ironically, many of the women in drag are actually played by members of Monty Python, who often play female characters.
 * In Zookeeper, Griffin (Kevin James) and Bernie the gorilla (voiced by Nick Nolte) sneak out of the zoo and go to a TGI Friday's (It Makes Sense in Context). How is it pulled off? Griffin simply has Bernie wear a shirt and they pretend to have come from a costume party. Works like a charm.
 * In Chitty Chitty Bang Bang, the Child Catcher disguises himself as a candy vendor by putting a coat on over his normal clothes. Yeah, that coat made him look completely different. But said coat was enough to fool Jeremy and Jemima, who had seen him earlier.
 * In She's the Man, it's fairly obvious when twins Viola and Sebastian (played by Amanda Bynes and James Kirk) are on screen together no one could possibly confuse them for the same person. However, it is lampshaded and justified in the beginning because no one at the school had seen Sebastian before. But later on, it becomes less plausible.
 * In Skyhigh, The Commander almost only differs from Steve Stronghold by the glasses the latter wears, as Layla points out...
 * This trope gradually came into play for the 1972 film adaptation of Sleuth.
 * Jason Vorhees (from Friday the 13th franchise, of course) may be one of the most iconic and most feared killers in slasher movie history, but he's also kind of stupid, especially in the second movie, where Ginny is able to convince him she's his mother, simply by wearing Ms. Vorhees' sweater. (Ginny looks nothing like his mother otherwise.) Yeah, it sinks in eventually, but given that it fools him for even a few minutes doesn't make him look all-too smart.