And yet, Ash and friends are tricked every single time.
Ringo Noyamano from Air Gear wants to help Ikki in his quests, but can't abandon her own team. She tries to Take a Third Option by disguising herself as a masked girl named "Croissant Mark" when going to Ikki's aid. No one is fooled.
One of the hobbies of All-Powerful Bystander Seravy (and occasionally his rival/love-interest Dorothy), whenever he's secretly watching from the sidelines in Akazukin Chacha. Ironically, everyone falls for it, except for Riiya , but nobody believes him anyway (or considering how powerful Seravy and Doroth are, it could be a case of "The Emperor's/Empress's new clothes).
Notice others using visual aspects of recognition, Riiya uses his nose, thus possibly is not fooled by any illusion magic if based on visual looks.
In Anpanman, any of Baikinman's disguises qualify as this. No one seems to notice that characters have shrunk (or grown in the case of the very tiny characters), feminine characters suddenly gain a more masculine voice, and no one notices Baikinman's sharp teeth and pink eyes, which are never covered by his outfit. This is made even more obvious on some disguises, where he even puts tape on his face (very obviously) to get a slightly chubbier appearance.
Koro-sensei from Assassination Classroom, being a giant octopus-like super creature, dons a fake nose, wig and gloves (and also changes his skin color) to pass off as a human. It works.
Averted and possibly parodied. When Japan visited Greece's land, Turkey attempts to spy on them donning a hooded green coat. It doesn't work.
In the anime, Italy uses the disguise of the 'tomato box fairy' upon meeting Germany. It doesn't work.
Also averted with England's fail attempts to escape from Italy. First time he tries to blend into the Italian crowd, his "disguise" consisted of his civilian clothing. He really wasn't trying to blend in all that much, especially considering how different the styles in Britain and Italy are. So of course he got caught. Admittedly his second attempt at dressing as an Italian improved but... you just can't hide those eyebrows.
It was less about the eyebrows and more about his behavior. He didn't chase skirts around like Italians were supposed to do.
In one episode of the anime, Germany tries to go around France's house, in disguise...by wearing a pair of glasses. France falls for this, at first, until he sees Germany mash his potatoes before eating them, as opposed to just eating them cut.
Germany and Prussia did a similar feat by taking American uniforms, in order to spy on America. Prussia plays this straight but, once again, Germany (wearing the glasses again) is nearly caught but, recovers by flashing an "American smile" and proclaiming that he "loves hamburgers!"
Oddly and ironically played with in Black Butler: In the second season some mysterious trenchcoat man (not only trenchcoated) appears at the Trancy Estate in the first episode. Ironic in the Latex Perfection that occurs in the slightly Alternate Continuity manga with the same character. It's Sebastian, by the way. Not that this spoils anything.
Euphemia tries to sneak through Ashford Academy's school festival by donning a hat and a pair of glasses. It doesn't help that she has waist-length pink hair. (Not that it doesn't work...)
She also manages to get away with this during an attack on a hotel by terrorists by hiding behind a pair of glasses. No-one notices her until she stands up and says who she is, despite being a princess, albeit one who hadn't debuted.
Code Geass plays this trope to hell and back given the ridiculous variety of hairstyles in the characters. Kallen has spiky crimson hair, yet her classmates fail to recognize her until she takes off a pair of sunglasses. An even more egregious example is C.C, who has massively long green hair, was not recognized by Suzaku, who had been searching for her on and off for two years at this point, because she had a bag barely covering her face. Though since the whole cast has got to have blue hair, this is less weird than one would think. These hair colors could very well be common in the Geassverse. There's also the fact that Kallen the student uses very different body language, wears her hair differently, and the fact that Milly was the only one who knew she was half-japanese. Not to mention the fact that Lelouch did figure out her disguise.
Tai and Izzy disguised Agumon and Tentomon by just giving them a hoodie and a hat and jacket respectively. And no one batted an eye.
Another episode has Piyomon and Sora's mom disguise themselves as Bakemon to save Sora. No one apparently notices, despite them being respectively shorter and taller than the others, and not being able to float. This is justified, since the Bakemons themselves have little to no brain power, and that everyone is busy with the fight between Lillymon and Dark Tyrannomon/Myotismon.
Dinosaur King has this being subverted, the Team Rocket-esque bad guys show up at on a game show pretending to be 13 year olds. However the Power Trio heroes not only see right through the "we're just really advanced looking for our age!" Blatant Lies but pretty quickly figure out who they actually are.
One of Doraemon's gadgets takes this to the extreme. It's literally just a board that you write someone's name on. Then you hang the board around your neck and anyone who sees it thinks you're the name you wrote. You can even write something generic like "servant" and have it work.
Dragonaut: The Resonance has Toa wearing glasses as a disguise during the year long period she, the former Dragonauts and their dragons were being hunted down by the ISDA. Sieglinde lampshades how ridiculous the disguise is.
The population of the universe are notorious for falling for these. During the original run, King Piccolo not only produced demon armies that killed hundreds but on live TV threatened to destroy the world, removed the rule of law and deposed the World Government holding them hostage. So what does he do three years later when he wants to enter the World Martial Arts Tournament? he calls himself Junior and wears a turban. Everyone falls for this. Lesser examples include Master Roshi passing himself off to his closest students as "Jackie Chun" by wearing a blue wig and Gohan not being revealed as a notorious vigilante despite his disguise consisting solely of sunglasses.
Well, to be fair, Goku figured it was Piccolo in disguise almost immediately and Ten Shin Han also was suspicious; moreover the crowd immediately recognized Piccolo as soon as he lost the turban. While Master Roshi used a wig, he also took out his glasses, something he never does in normal circumstances. He even gets a semi-finalist to pretend to be him in the crowd so as to show both of them in the same area. Yamcha figured this after their encounter and so did Master Tsuru during the second tournament. Finally, Gohan's classmates recognized him immediately as soon as he came out to the arena.
On the Gohan case, he initially wears a full headed helmet, not just sunglasses. This does not keep Videl from recognizing him instantly because of his voice. Later, he wears a turban with his sunglasses at the Martial Art Tournament (as wearing armor is prohibited) and the aforementioned classmate recognizes him as soon as he loses it.
Before adopting the Great Saiyaman persona, Gohan went Super Saiyan to create an impromptu disguise while thwarting a bank robbery. He goes the Henshin Hero route once his classmates (especially Videl) start suspecting he may be the "Golden Fighter".
Presumably, nobody outside the heroes suspected because Emperor Piccolo was killed at the end of the previous arc. Anybody who noticed the resemblance probably just thought Junior was somebody else of the same species, rather than the guy who ended up with a kid-Goku-sized hole where his heart and lungs used to be. How were they to know that Piccolo reincarnated himself at the moment of his death?
Not to mention that Emperor Piccolo was about 3 times larger than the (at the time) Goku-sized Piccolo Jr.
In a filler episode of the Red Ribbon Army Saga, Emperor Pilaf disguises Shu as Goku in order to infiltrate the Ox-King's village. The disguise consists of nothing but a giant plastic head that resembles Goku's. Everything else is exposed, including Shu's fur-covered hands and tail (he's a dog). Again, everyone falls for this. Granted, Goku has a tail of his own, but it's a monkey tail. Not something that's likely to get confused with a dog's tail.
Fairy Tail: In the third OVA, Natsu, Gray, and Happy avert this by putting on really convincing disguises while Erza and Lucy play it straight.
Randoll dresses up as "Prince Roscencruz" in Zero to return to Cyber Formula racing, complete with shades that resembles Knight Shoemach's sunglasses. Of course, Hayato recognizes him through the disguise.
Randoll also suggests Shinjyo and Miki to do the same in Saga as they join Union Savior, but the disguises fails in a split second because of Hayato and Asuka. Apparently, Randoll has taken this trope as his Running Gag.
Shoemach himself was one, as he does this to keep an eye on Hayato and his team to keep Smith and his men from stealing Asurada, but after the incident with Smith, it's been revealed that it is Osamu Sugo, Asuka's long lost brother in that disguise.
Vega from GEAR Fighter Dendoh has the sense to wear a wig and a completely different clothing style from her civilian identity in addition to her Char!mask, but it's still just a wig and a mask.
During the Renho arc, the Yorozuya gang and their allies don costumes to disguise themselves as Renho, which are actually convincing, save for Shinpachi, who instead was simply stripped down to his underwear, painted white, and had his glasses doodled on so they look like the eyes of a Renho. He naturally complains about this, after which they decide to have him ride on Kagura's shoulders...with the upper half of his body sticking out of a hole in the top of her costume. When a guard comes by inspect them and points out this oddity, they say he's a pimple, which prompts the guard to remove the "pimple" with a chainsaw, though it turns out he was only looking at Shinpachi's glasses...
The main trio often employs questionable disguises throughout the series, and at one point early into the show Gintoki and Madao were trying to fool Prince Hata just by making stupid faces.
In Guardian Fairy Michel, these are used most of the time by the Black Hammer Gang, but averted with Boogy's disguise in Episode 21.
Quattro Bajeena, better known as Char Aznable. He essentially trades out his mask for a pair of Cool Shades, and loses his uniform. In the end it really doesn't matter, since the Quattro identity was just established to keep people from immediately realizing that the Red Comet of Zeon had entered the Federation registry; in private with members of the A.E.U.G. he's pretty lax about it. It even gets a potential lampshade when he reveals his identity to the whole A.E.U.G., and Kamille's reaction is effectively "No duh." The fact that "Quattro" initially piloted one of the most Zeon-styled mobile suits in the A.E.U.G. and went out of his way to paint it red didn't help with the disguise.
Justified in the MSV-R manga. It's mentioned that there was a real Quattro Bageena who was a Federation soldier declared Missing In Action during the One Year War from the original Mobile Suit Gundam. Some corrupt Federation bureaucrats were selling the identities of MIA military personnel and Char simply picked out the most similar looking guy to himself he could find, so the disguise would only appear Paper-thin to people who had already met him as Char. And only a handful of people actually knew what Char looked like under the mask.
The Alternate Continuity manga Mobile Suit Gundam: The Origin tries to explain how Casval rem Deikun could pass as Char Aznable without being identified as the son of a famous leader. To that end it introduces a real Char Aznable, who is identical to Casval in every way except eye color. When Casval learns that the Zabis are trying to kill him, he rather cold-bloodedly swaps places with Char, taking his identity and letting Char get killed in his place. He then invents a medical reason why he always had to wear tinted lenses in the form of glasses or his Cool Mask to ensure that nobody ever sees his real eye color.
This was the base of a huge meme centered on a certain letter in Engrish that Kai leaves for the AEUG higher ups: "Captain Quattro, he is A CHAR!"
Gundam's Universal Century timeline has an even bigger example with the dummy balloon. The setting information says that due to Minovsky Physics, mobile suit targeting computers will scan an object's appearance, run it against a database of known models, and then substitute a CG image for convenience. This means that anything that vaguely matches the shape of a known MS will trick the computer, explaining how an obvious balloon could fool anyone.
This explanation is also used for Mobile Suit Gundam F91's final battle, where the F91's Super Mode involves shedding layers of its superheated armor to improve performance, which manages to fool the Big Bad even though he's sitting under a giant glass canopy.
In Turn A Gundam a group of people try to discredit Loran by attacking some towns with a Mobile suit "disguised" to look like Loran's Gundam. This disguise consists of nothing more then taping a mustache onto a FLAT. A FLAT looks like this. The titular Gundam looks like this.
It was probably helped by the fact that it was dark and foggy when they attempted this, so visibility was low, and most people had never seen the Gundam, only heard it referred to as "the Mustached Machine Doll".
Harry Ord, the resident Char Clone in the series at one point tries to go undercover on Earth. His "disguise" is little more than trading his odd shades for mundane eyeglasses and rather tacky engineer getup. Apparently it's enough for Loran and Dianna to not notice him.
Athrun Zala in Mobile Suit Gundam SEED Destiny attempts to gain a new identity after the war: Alex Dino. This absolutely does not work, as pretty much everyone who runs into him immediately recognizes him as Athrun Zala, though some play along out of politeness. It may have been a Shout-Out to the Quattro deal mentioned above, though.
Subverted with Mister Bushido from Mobile Suit Gundam 00: it was transparently obvious that he's Graham Akre from the moment he was spotted, but in-universe Graham isn't really trying to hide his identity, and even cops to it when his old friend Billy Katagiri meets up with "Bushido".
Gundam Build Fighters sporks this trope (as it does with many Gundam staples) with Tatsuya Yuuki and his alter ego Meijin Kawaguchi the 3rd. The Kawaguchi "disguise" is nothing more than a Badass Longcoat, a pair of Cool Shades, and his hair swept back (which was already one of Tatsuya's well-known Character Tics, done when he got pumped up during Gunpla Battles). Anyone who knew him as Tatsuya instantly recognizes him, and at one point Sei and Reiji confront Kawaguchi, leading to him giving a truly hilarious Suspiciously Specific Denial ("I know absolutely nothing about this Tatsuya Yuuki, who attended Seiho Academy and was president of its Gunpla Battle Club!"), while taking off his sunglasses and looking them in the eye. In one of the last episodes of the show, he hangs out with Sei and Reiji and openly admits that Kawaguchi is just him when he's "on the clock".
Chizuru's Sweet Polly Oliver disguise in Hakuouki completely fails to fool half of the Shinsengumi captains. Minor characters fall for it more easily but upon closer inspection, it falls apart just as quickly.
Hamtaro has Hero-hamwho is basically Boss in disguise dresses in straw hat, sunglasses, scarf, and cape, without even taking off his signature cap! In fact, Hamtaro only finds out his identity when he remembers that his voice is the same as Boss'.
Subverted early on, which sees the reclusive Nagi donning a mask and calling herself "Mask the Money", using her vast wealth to get Hayate out of a jam. Hayate sees through the disguise almost instantly, but plays along for the sake of Nagi's pride. When he accidentally lets slip he thinks Nagi's mask is silly, she explodes in his face.
Later it become something of a running gag, that every time that Maria dons disguise she is almost instantly recognized, but the other character either play along and/or think that she is cosplaying.
When Maria and Saki show up to distract one of the butlers during the school race, they expect to be seen through, but still go through the motions.
Both Klaus and Tama as well as Kotetsu are fooled into thinking Hayate is a girl when he's forced to cosplay.
Particularly notable when Hayate can see through a disguise as he's continually fooled by Paper Thin Disguises
Chiharu seems to be the only one who can pull this off, she's Sakuya's personal maid, as 'Haru' but she's seen by Wataru, Hayate and Nagi and they don't know it's her. Aika can see through it though.
Chiharu actively convinces Sakuya to allow her to play this one straight in Chapter 309 of the manga.
THE iDOLM@STER - Makoto dressing up as a boy so she wouldn't be recognized by her fans. It doesn't always work that well. Haruka also wears glasses and a beret to avoid detection.
When InuYasha is in public in the present, he generally wears a baseball cap to cover his dog ears. Never mind his anachronistic clothing and sword, lack of shoes, waist-length white hair, fangs, and claws. At one point someone comments he must be a cosplayer so maybe the paper-thin disguise isn't so bad.
Joseph Joestar of Jojo's Bizarre Adventure fame tries this in Part 2 in order to infiltrate a Nazi base. He literally crossdresses as a woman offering a bottle of tequila to the Nazi gatekeepers who were dragging other women into said base. Subverted in that the soldiers not only see through the disguise immediately but wonder what the hell Joseph was even thinking (As an aside, Joseph is over 6 feet tall, very muscular and broad-shouldered, and his "disguise" was nothing more than a bright pink dress and lots of make-up.) Even funnier is how Joseph cannot believe that his trick didn't work at all. So he just knocks the grunts out and steals one of their uniforms instead, which works better.
Joseph: Alright, damn, you Nazis are so smart! You saw through my disguise almost immediately... Soldier 1: Are you crazy!? Of course we saw through that thing! You're disgusting!! Soldier 2: Even my big sister isn't as ugly as you, and we used HER to plow the fields! She was an OX!!
Kamen no Maid Guy has Strawberry Mask, who's pretty much Liz wearing a riding helmet and pink lone ranger-style mask. Everyone knows it's her.
Subverted in Kamikaze Kaitou Jeanne where her hair colour and style changes and her eye colour. (And people STILL think she looks similar to Maron.
This is the primary running gag in the earlier arcs of Katekyo Hitman Reborn!. The titular character is (at first) the only toddler that the main cast knows who's capable of intelligent speech and simply manhandling the strongest of adults with ease. Yet every time he puts on a different pair of glasses or a fake mustache he seemingly becomes unrecognizable despite his distinctive size, hairstyle and baby face. Protagonist Tsuna is usually the only one who sees through the disguises, but the tables turn in a later chapter when he's the only one who doesn't recognize Reborn's adult self.
Hayato Fuurinji, Miu's Badass Grandpa enters a tournament intended for martial artists 20 and younger by putting on a Sentai mask and dubbing himself "Mysterious Teen Garyu X." Only Apachai is fooled. Worth noting, "Garyu X" entered the contest to ferret out another master who was hiding within his team for the purposes of winning. Then he just kept going for the hell of it...
Double subverted (or maybe just normally subverted): Garyu X is an incredibly thin disguise donned by the elder to compete in the 'age 20 and under' tournament, and of course everyone (except Apachai) can see through it immediately. The big flowing beard? It's uh... part of his mask! Right! However, it doesn't matter because the referee is the bad guy and decides to let him compete anyway for shits and giggles.
In an episode of Macross Frontier, Ranka, currently a hyper-superstar with posters of herself up all over town, manages to skip out on the huge parade she's supposed to be in and wander all over town undetected, cleverly hidden by a pair of big dorky lensless glasses. The other main characters recognize her easily and don't even comment on her "disguise," but no one else pays any attention to her, even though the whole city is trying to find her.
Sasami, when transformed, is only wearing a different outfit, and everyone apparently is fooled — at least until it is revealed it wasn't a secret at all. Still, her archenemy Pixy Misa only has a light Palette Swap, and no one can put them together...
Parodied in an episode where Washu shows up disguised as Santa in the middle of summer to help Pretty Sammy. Sammy sees through it immediately, but plays along as "Santa" gives a gift of a machine specially tailored for the situation and also places some diagnostic equipment on Sammy's forehead because "Santa likes to get scientific research". It's later revealed that Rumiya fell for it completely, though.
Completely blown through in the last episode, when her Mentor shows up in her classroom and addresses her as "Pretty Sammy" in front of everyone. It turns out that the entire class knew her secret identity but they didn't say anything because it was traditional for Magical Girls to have secret identities - they didn't want to embarrass her by mentioning it.
Negi and his students in the Magical World, being wanted criminals for a crime the villains committed, often disguise themselves in public by using pills to make them look five years older or younger than they really are and wearing Neko themed adornments such as ears and tails. They've yet to be caught. Of course, few Real Life people would look at a child when searching for a teenager. Later, they even get magical Clark Kent glasses.
Subverted by Natsumi, who is able to tell her adoptive brother Kotaro right off the bat simply by his personality and hairstyle.
Dr. Hell fabricated a cyborg seemed right like Prof. Yumi... except his nails were black. The reason why Hell did not strive to create a perfect duplicate is a mystery, but if he thought nobody would notice, tough luck because Sayaka, Prof. Yumi's daughter did. At least he did not make that mistake again when he fabricated cyborgs looked like Kouji Kabuto or his mother.
Apparently The Dragon Baron Ashura's Mooks can't tell the difference between Boss in a helmet and one of their co-workers. The mooks that were assigned to guard him and Kouji specifically, no less.
Though "The Phantom Renegade" already had a decent disguise, during the Tournament Arc a similar fellow named "Space Medafighter X", who wore the exact same (albeit gold plated) mask and used the exact same 'bot as the Phantom. Needless to say, it wasn't much of a "Reveal".
Not to mention the fact that the supporting characters did this too, dressing as "Space Medafighter X" whenever the real one was unavailable for some reason. And frankly, their disguises weren't much better.
Sonia and Cancer Bubble in the Ninja episode of the Mega Man Star Force cartoon, as shown here◊ (appears at 4:53 as they are standing with Geo and Luna).
Subverted in an episode. What initially appears to be the character Maddy in a Paper-Thin Disguise turns out to be the aged mystic Yahoot in an extremely effective disguise, which just looked like Maddy in a transparent disguise.
A straighter example is Commander Beef. The only physical difference between Beef and fish-peddling Masa is that Beef wears a cape and a helmet styled after a fish. Commander Beef wears a fish helmet. And they both wear an apron with a fish on it. In one episode in the anime, Lan makes the connection and calls him out on it. He is then dissuaded by Masa showing up while he's confronting Beef. A couple minutes later, 'Masa' removes his face, showing the face of Sal in a disguise, who then comments that she is not doing that again.
There's also his subordinates Black Rose and Mysteriyu. While Sal wears a Zorro-like mask and cape as Black Rose, Miyu as Mysteriyu has the worst disguise of all of them wearing only a big red bowl with eye holes over her head. But where the two girls really play this trope straight that They use the SAME NET NAVIS their civilian selves used in the N1 Grand Prix!
Maylu: They tried to fool everyone, but even a baby could tell who they were.
Mr Ando's penguin "disguise" in Mori No Ando is just a black suit... plus he's in the forest... Fridge Brilliance though because all of the other animals don't look much like their respective animals.
Konohamaru carries a blanket whose pattern blends into wooden fences. Or at least that's the idea.◊ Also, the portable "one-foot-tall brick wall".
Also Might Guy, despite being able to use transformation jutsus to alter his appearance, went out of his way to don a gray afro wig and an accompanying mustache in a filler episode in order to fool Rock Lee. Naturally, no one is fooled except for Lee.
Another filler episode involves two thugs dressing up (badly) as Might Guy and Rock Lee, and infiltrating the Leaf Village. In this case, Naruto is the only one fooled.
A flashback filler from Shippuden involved Naruto, Sakura, and Sasuke sneaking into a fortress run by cats by wearing cat-ear headbands.
Another flashback filler from Shippuden featured Guy in the same wig & moustache. No one is fooled except for Naruto, but Sakura & Shikamaru go along with the gag all the same.
Played straight during the Chunin exam arc, when Orochimaru is able to pass himself as a Jonin instructor from the Sound village (which he is actually in charge of!) by having a different hair do and slightly less snake-like appearance. He also passes as the Fourth Kazekage by hiding himself entirely in the Kage hat and cloak, which failed to arouse any suspicion. Beyond that, Orochimaru borders on Latex Perfection due to his unique and rather horrific habit of physically removing and wearing the faces of people he impersonates. Orochimaru is a strange case where this trope applies even with Latex Perfection. From his expression, it is really clear to that he is Orochimaru at least for the audience. The Abridged Series inevitably poked fun at this.
Orochimaru, Sasuke, Juugo, and Suigetsu casually walk into Konoha and manage to avoid getting caught despite only wearing hooded cloaks. Somewhat excused by most of the ninja being out of the village.
During the "Search for Tsunade" arc, Itachi (one of Konoha's most notorious missing-nin) and Kisame (a towering blue-haired man with distinctive gill-marks on his cheeks and sharp teeth) managed to stroll around Konoha and casual lunch without being noticed by anyone except for Kakashi, Kurenai, and Asuma. By wearing high-collared black cloaks with red clouds on them and straw hats. Said cloaks and hats actually obscure most of their features very effectively. Once they got past the guards by placing them under a genjutsu it was just a matter of not drawing attention to themselves, and they were still noticed fairly quickly.
Usopp adopts the guise of Sogeking, which doesn't disguise much and leaves his big nose obvious. All of his team members think it's ridiculous, except Luffy and Chopper, who are clueless enough to fall for it. It's so obvious that when Sogeking's wanted poster comes out, Kaya and the Usopp Pirates back in his home town immediately recognize him as Usopp. However the rest of the town doesn't.
Foxy the Silver Fox managed to fool Luffy simply by wearing a papier-mache head. Twice.
After the Time Skip, when, upon the real crew's two-year disappearance, a group of impostors pretend to be the Straw Hats. Despite their bad disguises and ridiculously different looks and body shapes, absolutely everybody is fooled - even some members of the real crew! Though given the fact that the Straw Hats were presumed dead after vanishing for two years, and would be expected to have changed appearance in that time, this trope may be Justified.
Usopp didn't happen to fall for any disguises, but acted surprised when the impostor imitating Sogeking showed up.
Chopper couldn't tell the difference until Nami and Usopp found him. Meaning he's either still really gullible or he's blind as a bat. In his defense, though, as a reindeer, he sometimes has a hard time telling humans apart and has to rely on things like clothes and hair color.
Luffy can maybe be forgiven, since he thought Fake Zoro and Fake Sanji were disguising themselves like he was to avoid causing a scene.
The same pirates all failed to recognize the real Luffy when he showed up right in front of them wearing a "disguise" that was nothing but an obviously fake moustache. The majority of his face however was covered by a hood, so it was somewhat Justified.
There are also a number of these on Dressrosa:
Luffy takes part in a tournament wearing some different clothes, a helmet, and a fake beard. It could be considered to be an adequate disguise - although several people see through it from the start - but not when he starts to use his Gum Gum powers in the ring, which should be a dead giveaway of who he really is... yet most people still do not recognize him!
In the same arc, Jesus Burgess, even with his ridiculously identifiable body structure, is able to hide his identity from the others with nothing but a paper bag - a literal paper-thin disguise! - over his head. Then again, competitors that bulky in that tournament were a dime a dozen.
And again on Dressrosa, Franky, a nine-foot tall blue haired cyborg, successfully fools the enemy by wearing a towel over his head.
Remarkably, this works to Luffy's advantage. The disguise is so general that it allows Sabo to take his place without anyone knowing any better.
Law, on the other hand, totally changes his outfit, wears sunglasses and a fake mustache, and wears a trench coat with a hood he keeps up. Except the coat is open and he's not wearing a shirt, showcasing the massive tattoo on his chest that includes his distinct Jolly Roger in the design. His hands, which also are tattooed in a very distinct way that relates to his pirate name, are also uncovered.
On Whole Cake Island Caesar Clown tries to pass himself off as "Gangster Gastino" of the Firetank Pirates. While he has a completely different outfit and hairstyle, absolutely no one, not even Luffy buys it. It's even lampshaded by his Boss Subtitles!
The Straw Hats' attempt to sneak into a Navy base during the anime-only Navy Supernova arc features a lot of this. Of the four infiltrators, Nami's the only one who wears a thorough disguise, and even that fails because she does nothing to hide her face. Chopper's disguise as a burly marine gunner would be convincing if it weren't for the fact that he's still clearly an animal person, Carrot doesn't do anything to hide her rabbit ears or tail, but Luffy's by far the worst of the bunch; he wears the Navy's Coat Cape and that's it.
Both included and subverted in Otogi Zoshi in which the female protagonist spends half the first arc in male drag. It fools random grunts and obnoxious nobles, but Seimei, Sadamitsu, Urabe and some minor characters pretty quickly figure out that she's a girl wearing pants.
During the physical exam episode of Ouran High School Host Club, Tamaki disguises himself as Haruhi, so nobody finds out he's really a she. His disguise consists of...putting on a wig. Everyone sees through it immediately.
This is one of the defining characteristics of Team Rocket. The "twerps" don't know it's them until one of the trio starts the motto (or accidentally starts it upon hearing the motto's words out of context), even when it's painfully obvious to a casual observer who they are. To be fair, sometimes they really do put on some good disguises (including of the other gender). However, more often they simply don't, and in any case they very rarely disguise their voices and distinctive hairstyles. Given that they show up Once per Episode, you'd think the heroes would be intimately familiar with them.
James' disguises are usually good, especially when he crossdresses. The problem with Jessie's is that she almost always keeps her long red hair. But Meowth is easily the greatest user of this trope, all he needs is a baseball cap, t-shirt and shorts and suddenly he is a human student. What about the feet? The whiskers? The paws? THE TAIL?! Ash must have some serious vision problems...Here the list of all of them.
Since Jessalina is Jessie (props for switching Contest disguises when they got to Sinnoh), she actually beat Dawn in a contest!
Played with in an episode which has James dressing up in Jessie's contest disguise to take her place when she is sick. Everyone is still fooled. He even wins!
Subverted in "Holy Matrimony!", when Jessie and Meowth wear all black to become "invisible"; James' family pretends to be fooled by it.
Not so much pretending as following custom - the black outfits are based on the assistants in traditional Japanese theater, whom are considered to be "invisible" by the cultural rules of the theater. Of course, this is something a Japanese viewer would understand natively, but gets Lost in Translation when exported.
Subverted in another episode where Team Rocket decides to help the protagonists. They don their usual style of disguise, help them and then go on their merry way believing they fooled them...then Misty says goodbye by shouting "Thanks, Team Rocket!" Ironically, that was their first attempt. Ironically they were disguised fairly well there.
Subverted in the Johto episode "The Heartbreak of Brock"; Misty is immediately suspicious when she sees the disguised Team Rocket, even taking off Jessie's disguise glasses to prove her suspicions.
Played with interestingly where Meowth dresses up as a Shiftry. While it initially works (despite the 3 foot difference between the two Pokémon species), having never seen one before, Dawn scans the "Shiftry" with her Pokédex which then proceeds to give her the entry for Meowth.
In a Hoenn episode, Meowth and Jessie attempt to disguise themselves as Kirlia and Gardevoir, respectively, in an attempt to grab a Ralts that Ash and friends were taking care of. Ash proves that the Pokédex is disguise-proof by scanning the "Kirlia" and getting the data for Meowth instead. So much for that disguise.
In several episodes Meowth disguises himself as a Sunflora by taping his eyes shut and holding cardboard leaves.
The worst offender was an early Diamond and Pearl episode in which they pretended to be traveling salesmen...by putting on green jackets over their uniforms...and not even zipping them up! Ash and co. somehow fail to spot the enormous red "R"s on their chests, even though they couldn't be more obvious.
The above post may be forgetting the episode in which Team Rocket dresses Meowth up as a Croagunk in order to win a contest revolving around them. This is an entire town, a freaking Gym Leader among them, all of which are obsessed with this particular Pokémon to an almost creepy level (and in the case of Brock, actually owns one), and they are not only fooled down to the last person, they actually consider him the best looking one of the bunch.
Subverted in Fire and Ice by Brock when Jessie pretends to be Nurse Joy. "My beloved Nurse Joy's lips actually move when she talks!" Brock is known to have the unique ability to tell all of the apparently identical Nurse Joys apart at a single glance, which is probably why he wasn't fooled.
Lampshaded at the beginning of "Pursuing a Lofty Goal", when James, in a suit and dark sunglasses, curls up in a ball when he first sees the twerps. When they ask if something's wrong, he remarks in an aside, "I forgot, the twerps wouldn't recognize me if I paid them!"
In two Hoenn episodes, Team Rocket disguised themselves as May's family. In one episode, it was just James disguised as Norman, whereas in the other even WOBBUFFET played along. James was Norman in the second episode, while Jessie was Caroline, Meowth was May, and Wobbuffet was Max.
Possible the most blatantly disguise was when they dressed up as VIKINGS in the first movie. The fact that A. vikings haven't been around for about 1,000 years and B. they never were in Japan, barely crossed their minds ("I didn't know the Vikings were still around!" / "They mostly live in Minnesota!")
Played with in XY012 — in an attempt to trick a Vivillon seller to leading the kids and Officer Jenny to his hideout, three characters try on a Spewpa disguise for bait. Ash is this trope and admits he wouldn't fit in the cage anyway. Dedenne fares a bit better, but is more Scatterbug-sized than Spewpa. Chespin is the most accurate aside from the pupil eyeholes and saying its name.
Played with to a bizarre degree in the penultimate episode of ''Best Wishes": While Jessie attacks, James disguises as a recurring character named Porter, in order to trick the twerps and take their Pokemon. His disguise is actually good. But in order to avoid suspicion in Jessie attacking them alone, she disguises the left half of her body as James. She'll turn her body one side to say her lines, hiding her James side from the twerps, and doing the reverse for James' lines. It's downright absurd.
In one episode Serena disguises herself as Ash because a one shot character of the day is demanding a challenge when Ash is feverish and won't go away. The disguise consists entirely of wearing his clothes and attempting to hide Serena's hair under his hat (which works, but mostly because of her newer shorter hairstyle, the early season Serena could never have pulled this off). It still somehow fools the character of the day, even though he'd literally been talking to Serena a minute prior so he failed to recognize the same girl who left and came back a minute later in different clothing, and even Team Rocket is initially fooled, but they eventually figure it out. Clemont and Bonnie however, instantly can tell it's her, although she quickly gets them to keep up the ruse. To be fair though, a big part of the disguise is simply the demure Serena pulling off a pretty spot on impression of Ash's louder dynamic personality.
Pokémon Adventures has Looker do this late in the Black and White arc, donning a pair of glasses with a fake nose while claiming to be named "Lou Karr" ("Handa Samuro" in the Japanese version) as he participates in the Unova League.
The titular Princess Tutu and Princess Kraehe both don Paper Thin Disguises as (or perhaps are the Paper Thin Disguises of) Duck and Rue, respectively. It's somewhat understandable for Duck, since no one would ever expect the worst dancer in school to be the "goddess of dance", and only the characters from The Prince and the Raven seem to be able to see her in human form anyway, as everyone else just sees her as a giant swan. The only difference in Rue's appearance (besides the infallible change of costume) is a different hairdo, and her motives are fairly obvious to everyone around her, too. Maybe it's the local Perception Filter at work.
Ranma is frequently able to fool Ryoga into believing he is anyone up to and including Ryoga's own sister (Ryoga doesn't have a sister) with little more than a change of clothes and occasionally hairstyle. To be fair, everyone in his family has such poor sense of direction that they hardly ever see each other, though he still doesn't have an excuse for every other time he fell for it.
Ranma has fooled other people with Paper Thin Disguises as well. For example, in the manga, he pretended to be Soun's wife in order to trick Hinako into giving Soun up. He was successful with nothing more than an apron and something akin to a bandana.
Ranma even lampshades this trope from time to time by remarking how he's surprised his disguise worked so well or thinking about what an idiot Ryoga is for falling for it.
In one arc, Shampoo and Kodachi wear glasses in order to fool Hinako.
Rave Master: "You seem to have mistaken me for someone without a hat".
One of the more infamous examples, the girls essentially wear uniforms similar to actual school girl uniforms and not one of them wears even a simple mask. Yup, no masks, no hair color changes, pretty much nothing concealing their identities. Despite this, no one seems to recognize Usagi and her pals. This is particularly worse for Sailor Moon herself, whose Sailor outfit and school uniform not only share the same colour scheme, but she wears her transformation brooch on both - not to mention that rather distinctive hairdo. A few of the characters are occasionally recognized not by appearance or voice, but by performing actions or behaviors unique to them. For example, Minako is id'd by an old school friend because he recognizes the way Sailor Venus plays volleyball to be the same as Minako's.
This is particularly frustrating during arcs where the villains are actively seeking Sailor Moon's true identity, but constantly fail to recognize Usagi even though she looks exactly the same. Kunzite is the worst at this, as he frequently came up with elaborate plans to track down Usagi, but despite technically luring her in every single one, he frequently picked the wrong girl anyway because he somehow didn't recognize the girl with the same hair, voice, and catastrophic clumsiness.
Minako wore a mask in her days as Sailor V, though it doesn't hide the fact that she has the same hairstyle and even retains the same bow in it. In Codename: Sailor V, however, she actually is recognized. Sailor Moon originally had a similar mask in the manga, though she essentially stopped using it past the first act and it has the same problems as Minako's.
The Senshi even have trouble recognizing each other if they haven't been introduced in civilian form. Minako doesn't recognize the other four Senshi at first outside of their transformed states. Later, in S, despite interacting frequently with Haruka and Michiru in their civilian forms, they do not recognize them as Sailors Uranus and Neptune until they are told as much later. Similarly, Haruka and Michiru don't recognize the other Sailor Senshi out of uniform.
The villains do this as well. For example, Jadeite is only seen to try to disguise his physical features once during his entire career in the anime, and he frequently goes under cover using variations of his actual name. In one instance, he went as a D.J. named "J. Daitou". The English dub even got into the act, as his name was "Jedite" in that version and he called himself "Jed" on at least one occasion despite not disguising himself aside from changing his clothes. What makes this even more frustrating is that the villains don't really care about maintaining their disguises. When their evil scheme of the week is figured out, they usually change right in front of the heroines, only to be completely unrecognizable again to them the next episode. Even worse considering that some of them never really change their civilian outfits.
Averted in the live-action adaptation, where the Sailor Senshi look like normal Japanese girls in their civilian forms, then actually change to their colorful and over the top anime hair when they transform. The villains are also more effective in tracking them down in this version regardless.
This is much less prominent in the manga, because no one actually gets a good look at the Senshi. The victims are usually unconscious or stuck where they can't see the heroes, and even surveillance cameras just seem to record blurs around their faces. It should be noted that the manga is much shorter than the anime in terms of storyline, so there aren't as many opportunities for people to see Sailor Moon and co. On the rare occasions that people who actually know them meet them in their transformed states, they frequently identify them immediately. Most of the villains recognize the Senshi in their civilian states on sight as well, and in fact frequently target the girls directly. As few of the manga's villains show up past their first appearance (frequently getting killed in one go), the Senshi also get no opportunities to conveniently not recognize them after they've been ID'd.
Played straight in Samurai High School with the sakakido twins who by circumstances must swap gender roles or face exile... which is hilarious since not only the sister is two feet taller than the older brother, like 36DD, ankle long hair and is a Master Swordsman while the brother is a pocket size Quintessential Yamato Nadeshiko but it takes a girl with supernatural analytic abilities to just realize the difference. Of course nobody believe her.
Kyatto Ninden Teyandee / Samurai Pizza Cats plays it even more straight than Sailor Moon. The Cats in question go through an overly long and elaborate transformation sequence where the only things that are changed are some pieces of their street getup with something more combat capable. Made all the worst in that their departures after their change are publicly broadcast from the pizza place that has a giant gun that shoots them out and the fact that they still call each other by their full names in combat. Yet no one in the series clues in unless they're a part of the "secret" conspiracy. Granted it's an over the top parody but not a single person catches on that the Yattaro / Speedy Cerviche fired from the giant gun and the Yattaro / Speedy Cerviche that runs around delivering pizzas from the same place are the same.
Science Ninja Team Gatchaman episode Gatchaman Secrets Stolen. A scientist working for the ISO steals important secrets for Galactor. The team is given the job of stopping him. Their civilian identities are Dr. Nambu's wards/adopted kids who are allowed free run of the place, and most of the scientists recognize them by sight, if not name. G-1 decides to disguise himself as the Galactor contact for the scientist... by putting on a pair of sun glasses. note The situation is even more absurd if you've seen the episodes that outline that the team has to wear a particular set of civilian-mode clothing in order to transform to battle uniforms; ergo, the team wears the same clothing nearly all the time.
In Sekirei Musubi recognizes Kagari from behind, until she looks at his face and says that he isn't Kagari because "Kagari doesn't wear a mask."
Parodied in The Seven Deadly Sins's tenth episode, where Meliodas and Ban, both "Wanted!" Poster bandits, have signed up in a fighting tournament under the guises "Meliodaz" and "Baan". One of the other contestants believes himself to recognize them from the posters... but dismisses the idea, since their names are different.
Sgt. Frog has The "Pekoponian Suits". Keroro and his squad of frog aliens disguise themselves by using robot bodies. Their heads, which look nothing like a human, are completely exposed.
All the Terrible Trio in Time Bokan series, but The Doronbo Gang, from Yatterman are masters of this. They're never recognized despite the fact that both Tonzura and Boyacky never remove their goggle-style masks, and Doronjo always wears a masquerade style mask. Not to mention the buildings they set up to create scams always have a red skull as part of their decor.
Sometimes Gan and Ai are smart enough to notice, but always just a bit too late to prevent them from scamming a ton of people and then launching a new mech.
Speaking of Gan and Ai, The Doronbo Gang are never aware that these two teenage kids dressed in jumpsuits that seem to show up everywhere are actually Yatterman in civvies.
In a chapter of Urusei Yatsura, we see the kunoichi Kaede (now branded as a nukenin) trying to find jobs after quitting ninja school. But, as a nukenin, she must be hunted down and killed, so she has two pursuers in the forms of her childhood buddies Kumade and Mukade. At one point, she adopts a disguise to evade them and Ataru (whom she keeps running into): a pair of glasses. No fake nose and mustache with it, just the glasses. At the same time, we see that her pursuers have also taken jobs in the same inn Kaede is, and that they too are wearing disguises: Mukade (the long-haired one) wears a mask on her lower face, while Kumade (the one with an eyepatch) just has a striped eyepatch in place of the one she usually wears. The worst part of it is, the three walk past each other in a corridor... and are unable to recognize each other!!! Ataru, however, isn't fooled, and ends up inadvertently giving Kaede away.
In the Legendary Hero's arc, Jonouchi doesn't realize that "Madame Butterfly" is actually Mai at first, even though her only disguise is a butterfly shaped domino-mask that does nothing to change her voice. (After she uses a Harpie Lady card, he manages to put two and two together.)
In the KC Grand Prix arc of the original series Yugi's grandfather disguised himself using his bandanna as a mask. Needless to say, only Joey - his opponent - fell for it. The rest simply didn't want to ruin Solomon's fun. (In the dub version, it was even more obvious; the name he used was "Apdnarg Otum" (which is just "Grandpa Muto" spelled backwards; he called himself "Mask the Rock" in the original version) and nearly gave himself away with what he said more than once.)
During the first season of Yu-Gi-Oh! GX, the Dark Scorpions tried to infiltrate Duel Academy by disguising themselves as faculty (or a student, in one case). Exactly why this didn't initially raise suspicion isn't clear, seeing as they didn't seem very convincing. (Especially in Meanae's case. She posed as the school nurse, and Duel Academy already had one.)
There was apparently a sale at the generic gray cloak shop during Season 3 of GX, as at least five separate characters don them.
In Yu-Gi-Oh! 5D's, all Dark Glass has to do to differentiate himself from Bruno is change his hairstyle and don some red sunglasses. Despite the fact that they're both mysterious blue-haired D-Wheel experts who showed up at around the same time. And both were left-handed, no less.
There is some "mystery" about who the "Masked Fighter" is during the Dark Tournament. Despite "him" being the same size as Genkai, who is so short as to invite Lampshading. And having the same moves, down to the one-of-a-kind super move only Genkai knew. And there being no one else competent who would show up.
But the trope ends up subverted when the fighter's mask falls off, revealing the face of a young woman who nobody has seen before. It's actually a Double Subversion, though; the young woman is Genkai. Reikohado-ken reverts the body's cells to their most powerful state whenever it is used, and naturally, her peak was in her youth.
To his credit, Kuwabara was positively convinced Mask (as the Urameshi Team called their teammate) was Genkai, but The Unreveal caused him to change his mind. When the mask comes off again and it really is old lady Genkai beneath it, due to her giving her powers to Yusuke, Toguro comes up and explains everything for the benefit of the demon audience which think the Urameshi Team was cheating.
Lampshaded in the English dub by Koenma, "C'mon Yusuke can't you see through a simple disguise?!" Jorge is wearing a bodysuit with his initials on it, Koenma is cosplaying as Tuxedo Mask, and Botan is wearing a cloak and glasses.
Nearly every disguise in Galaxy Angel, like Vanilla wearing a handlebar mustache without hiding her ringlets or Millefeuille wearing an enormous bow-tie with a Coat, Hat, Mask.
Played for laughs in Punchline. The fact Mikatan is the superhero "Strange Juice" is incredibly obvious however her neighbors don't realize it until they see Strange Juice without her mask.