Lorne's overcoat and a trilby, which looks dashing in a Humphrey Bogart-sort of way, but about as inconspicuous as a Ninja Turtle.
A baseball cap and sunglasses are enough to disguise him in broad daylight.
Naturally, Lois and Clark used this with Clark simply slicking back his hair as Superman. A famous bit has villain Tempus revealing the truth to Lois and how people in the future ask "How dumb was she?"
In one episode, Lois gets super-powers and becomes the masked heroine Ultra Woman. She's amazed at how a domino mask is all that keeps Perry White and Jimmy Olsen from recognizing her, ranting about how they can't see the truth of someone they work with every day...and stops when Clark smirks at her.
Buffy the Vampire Slayer: Buffy gets rather miffed that her friends thought the Buffybot was really her going through grief. Also Played for Laughs at the beginning of Season 6 when it goes to Parent-Teacher Day and no one notices the difference. In a Fridge Logic moment, the Buffybot is able to impersonate Buffy well enough to fool Glory, despite the fact that Willow was unable to get the same result after months of tweaking during the summer.
Hannah Montana has the title character, who is able to complete conceal her identity by simply wearing a blonde wig; in one episode, she dramatically removes the wig to reveal herself to her boyfriend, and he's totally shocked, despite the fact that "Hannah" didn't change her clothes, make-up, or facial features in the slightest. Other characters suffer from this too, including Robbie Ray, who's apparently disguising himself with a (thin) mustache; however, this might be a subversion, as Robbie isn't trying to conceal his identity as much as his daughter.
It's lampshaded when Miley reveals herself to the world as Hannah and genius neighbor Rico nearly has a breakdown figuring out how he couldn't see through such a lame disguise.
Many episodes of I Love Lucy have Lucy and Ethel dressing up in paper-thin disguises to fool their husbands in some scheme. Depending on what the plot demands, Ricky and Fred either are completely fooled or recognize their wives right away.
Tennessee Ernie Ford doesn't recognize the Wicked City Woman trying to seduce him (just Lucy in a black wig).
The Blackadder Goes Forth episode "General Hospital" features Blackadder trying to find a German spy in the field hospital. One of the men recovering there has a very thick German accent, introduces himself simply as "Smith" and behaves rather suspiciously...Subverted in that as Blackadder points out, not even the Germans are stupid enough to send a man with such a pitiful disguise to be a spy; he's actually a British spy who's been in Germany for so long he's developed an accent.
Similarly, George's suggestion that they find the German spy by going to the hospital and looking for the person whose name begins with "von" receives understandably short shrift from Blackadder.
Similarly, in "Major Star", Private "Bob" Parkhurst is just a woman dressed up in men's clothing, without any facial disguising at all, and yet she is able to fool the General into thinking she is a man, to the point where he is repulsed by her "disgusting drag act" when she gives a cabaret performance (as opposed to earlier, when he thought George's actual drag act so real, he tried to date "Georgina"). Edmund, on the other hand is not fooled for a second, telling "Bob" "You're a girl with as much talent for disguise as a giraffe in dark glasses trying to get into a "Polar Bears Only" golf club."
"Bob"'s ancestor, Kate (which she says is short for Bob), does something similar in Blackadder II. Everybody is actually fooled by it, though Edmund falls for her and is worried that he might be gay. It's only when she shows Blackadder her breasts that he realises that she's a woman.
In Blackadder The Third, the Prince of Wales and his butler exchange clothes and fool everyone, even their Igor, Baldrick or the King, the Prince's father.
To be fair, the King in question was a complete nutter, Baldrick was a complete idiot, and the entire setting is a Crapsack World where the character of Blackadder is typically the Only Sane Man (with the exception of the first season).
This is theoretically actual history this is taking place in, so the fact that the king is off his nut shouldn't come as a surprise-he's George the Third.
In "The Witch-Smeller Pursuivant" in Blackadder I, Blackadder goes King Incognito to avoid detection while he consults a wise woman. His disguise consists of a leather strap across his face. However he is recognised by a Peasant, despite people referring to him as 'Stranger'.
In "The Archbishop", Blackadder is chased by a pair of crusaders and he, Baldrick, and Percy disguise themselves as nuns to shake them off. The disguises not only work fine, but the crusaders subsequently decide to put on similar disguises as well in order to fool Blackadder and his company. They follow with a short discussion, neither side realizing the truth - even though one of the crusaders has a beard! - until they accidentally thank one another without a high pitch.
Used in the Farscape episode 'Coup by Clam'. A female character has disguised herself as a man by covering up her breasts in spite of the fact that her face is completely unchanged. She manages somehow to fool the guard she works with (possibly justified by the guard being an idiot as well as a misogynist dickhead) but Chiana sees straight through it. Also used again in that episode with John dressing up amusingly as one of the least convincing women ever, in order to enter a club where all the male clients are known.
Subverted in an episode of M*A*S*H where Colonel Flagg comes into Radar's office wearing a pretty absurd disguise, and Radar recognizes him quickly. When Flagg sternly asks him how he recognized him, Radar nervously said that Flagg was so good at not looking like himself that he guessed that someone who looked so much not-like him must be him. (However, when Flagg then walked into Colonel Potter's office, it didn't fool Potter either.)
On Doctor Who, the Master, whose skills involved being a master of disguise, disguised himself frequently during Roger Delgado's tenure with a pair of glasses. Anthony Ainley also adopted paper-thin disguises in "Castrovalva" and "Time-Flight" (In the latter case, they actually intended to fool someone, as Ainley even used a pseudonym in the credits). The Master hid behind pseudonyms like "Colonel Masters", "Mr. Magister", "Dr. Masterly", etc. In the new series, he hides behind an unintentionally Significant Anagram.
To be fair, in most cases the Master was trying to fool ordinary people who at that point had no idea who he was or what was going on (often his schemes involved infiltrating organizations under false identities), and his pseudonyms are probably intended to be bad as a mockery of a species he looks down on. In fact most of the time whenever the Master appears in disguise to the Doctor or someone who actually knows who he is they see right through his disguise immediately (and he probably wouldn't have it any other way).
In The End Of Time he even lampshades it, sort of.
In "The Visitation" (Peter Davison Doctor) the villain travels to London wrapped up in a huge cloak. Seeing as he's a lizard-like alien with nothing covering his large green snout this disguise is particularly unconvincing.
Madame Vastra is a Silurian living in Victorian London. Despite her only cover being a transparent black net veil over her head, nobody seems to notice that she's got green scaly skin and bone frills unless she specifically lifts the veil to show them.
Subversion: On Top Gear, the presenters occasionally switch out James "Captain Slow" May for their "tame racing driver", a masked man known only as The Stig. The whole disguise is The Stig wearing one of May's iconic shirts (a ghastly purple-and-pink striped number) over his white racing suit. Mysteriously, no one finds it convincing.
May: Some say I was bound and gagged in locker room...
Also played with during the Hammerhead i-Eagle Thrust challenge when the "independent tester" was clearly May with a gaffer-tape mustache and his hair tied back.
And in the "Three Wise Men" special, when Clarkson and Hammond dress up in niqab. For one thing, Clarksons is six foot five.
In Glee, the kids switch names to screw with the substitute teacher. What name does the blonde, female Brittany choose? Mike Chang.
Someone handed MacGyver the Idiot Ball in the episode "Cleo Rocks". Despite clues so obvious that a child could work it out, it takes Mac most of the episode to realize that his old nemesis Murdoc is back, even though his disguise is so thin that it's obvious who he is the first time we see him. From behind. In the dark. And he's only halfway in the frame. They clearly thought it was working, too, since even after the first reveal where Murdoc appears undisguised, it's only after we get a second reveal that anyone realizes that he's been in disguise all along.
More like the producers expected the audience to be carrying the idiot ball. Since it was airing on USA network at the time, they were probably right.
From 'Allo 'Allo!, there is the character of Monsieur Roger LeClerc, "Man of a thousand faces - every one the same." Most episodes see him donning a completely useless disguise and conspiratorially whispering "It is I, Le Clerc!"
Subverted: A 'Duck Seller' enters the café approaches the bar and identifies as Le Clerc, but Le Clerc pops up and outs the Seller as an impostor. It is in fact Mme. Edith in a very convincing disguise.
In Leclerc's case, Rene almost always recognises him immediately. However, when events like the Colonel and the Captain being trapped as British POWs in a Stalag Luft, and examined closely by their own General, or Herr Flick posing as a temporary typist, Gruber or the airmen (complete with large handlebar moustaches) posing as nuns, and going completely unrecognised, the trope is played much straighter.
As mentioned, Gruber's disguises are usually pathetic, but one episode features him disguised as a nurse so convincingly that most viewers don't realise it's him until he speaks. Judging from the explosion of laughter, the studio audience didn't recognise him either.
Beautiful subversion on Arrested Development, where Tobias steals the plot of Mrs. Doubtfire and dresses himself up as a British nanny in order to try to get closer to his daughter - complete with Mary Poppins-style song-and-dance numbers and Tobias' own total lack of competence at housework. The other characters, apparently far more Genre Savvy than Tobias himself, recognize Tobias right away, as well as the movie he took it from, and their trying to deal with this without breaking Tobias' heart create some of the show's most hilariously painful scenes.
The best part is that in order to impersonate a woman, David Cross had to shave off his signature mustache - thus, whenever Tobias reappears as himself, he's wearing a painfully fake mustache.
In the infamous "pizza episode" of Power Rangers Turbo, Porto comes into the pizza parlor to pick up an order, wearing a dress and large woman's hat to disguise himself. (Given his natural shape, which resembles a man in a bulky spacesuit, it's not very convincing.) Not a completely straight example of the Trope, because the clerk does seem to notice something odd about him, and when Porto notices that the Rangers are there (in their civilian identities), he leaves quickly before they see him.
Terryin Al Murray's Time, Gentlemen, Please! is frequently able to pass himself off for someone else just by wearing different clothes, an obviously fake moustache and in some cases simply saying he's not Terry. This doesn't last for long however since Terry is known to be 'very gassy'. He is however hailed as a master of disguise by everyone he fools.
Unintentionally averted in "The Night of the Avaricious Actuary", when Artie is disguised as a gas company meter man; he broke his leg during filming of the episode so he was replaced for part of the climax by a stand-in (who looks nothing like Ross Martin).
In the film version, however, it's much much worse. Gordon is introduced disguised as a saloon girl... and despite looking rather obviously like a man, and sounding very little like a woman, his disguise fools the living Hell out of everyone. Yet, even this is topped when James West dons an awkward harem costume and interrupts the villain's inaugural Nebulous Evil Organisation meeting by doing a Little Egypt dance, which despite being membrane-thin and a grossly obvious diversion tactic, somehow gains the rapt attention of every bad guy in the scene.
Of course, the movie also played it perfect with Gordon's spot-on Ulysses S. Grant impression. (The fact that Grant was played by Kevin Kline as well helped a bit, too.) He still can't fool West, however.
In fairness, Artie was also occasionally disguised as a woman on the original show as well ("The Night of the Freebooters" and "The Night of the Green Terror") but never to that extent.
Eric van Helsing from Young Dracula who doesn't even shave his beard off when disguising himself as a woman.
Kamen Rider Black plays it painfully straight with the main character. Now, while a suit that covers one's entire body is good for hiding one's features, Kotaro has a habit (shared with pretty much every Rider ever, actually) of using his Rider-motif bike in civilian identity. He gets a new bike as Black, and rides it in civilian form, too. Establishment shots frequently have it parked outside in plain view. He never tries to pretend to not be hunting down whatever Golgom is up to, or ever make an excuse for running off. Somehow, nobody notices.
Inverted in Kamen Rider Double in that, while Shoutarou rides around on the same bike that Double uses, the Fuuto Police Department inspector believes that Shoutarou is a 'friend' of Double. One could assume that he also told the inspector that Double gave him a duplicate bike and that the public simply also believes this.
Parodied in a Monty Python's Flying Circus sketch, where "Mr. Hilter" and his associates, "Ron Vibbentrop" and "Heimlich Bimmler", campaign for the National Bocialist Party in Minehead, England. Nobody recognizes them, despite wearing Nazi uniforms, speaking in thick German accents, and denying that they're Nazis rather unconvincingly.
Heinrich "Bimmler": I am retired vindow cleaner und pacifist, without doing war crimes.
In the costume party episode of Taxi, Jim apparently fools everyone by going just wearing his usual outfit. However Alex notices and he puts on a pair of novelty glasses.
Mystery Science Theater 3000 subject The Rebel Set features one of the most bizarre examples of all time: the mastermind of an armored car robbery goes incognito on a train to bump off his henchmen (all of whom have spent a lot of time with him) and keep the money for himself. His disguise? A priest's collar. The MST3k guys have said that the first time they saw the film, it took them all quite a while to realize it was even supposed to be a disguise.
In the Cloris Leachman episode of The Muppet Show, pigs take over the show and fill all the roles. Cloris comes out on stage while "Kermit the Pig" is making an introduction and states her belief that he's not Kermit the Frog, despite being green (not easy for a pig) and having the collar. What changes her mind? "Ribbit!" He didn't even have to hide his ears or snout.
Any role played by Gonzo fits, as the mask has to fit that unique nose of his.
Gonzo: (As the Black Knight) The world will forever wonder who I am! Kermit: Though some may harbor suspicions...
Beaker once donned a lampshade to hide from testing Dr. Bunsen Honeydew's invention. This worked well, until Beauregard plugged him in.
Bunsen takes a turn while being harassed by multiple clones of Beaker, trying to hide his identity using a Conspicuous Trenchcoat, a hat and a plastic glasses/nose/'stache arrangement. It fools Kermit but works for all of thirty seconds before the Beakers find him.
In the episode with Milton Berle, Fozzie is afraid of meeting his idol and hides throughout the show. At one point, Fozzie wears a disguise, which is merely a pair of glasses with a fake nose and large beard attached. At first Scooter appears to be fooled, but then it's revealed he isn't.
In Tales OF the Tinkerdee, a pre-Muppet Show Jim Henson production, Taminella Grindenfall, witchiest witch of them all, is able to disguise herself as a Santa Claus, the princess, the kingdom prime minister, and an artist by wearing different wigs and hats.
Zigzagged in the Muppet special Hey Cinderella!. As the King plans a masked ball, Prince Arthur Charming meets Cinderella while gardening and, after realizing she doesn't recognize him as the prince, says he's the gardener. He arranges for everybody to be invited to the ball so she can go, but since it's a masked ball they arrange to each wear a geranium so they'll recognize each other, unaware that the King plans to give each guest a geranium. They end up spending the whole time at the ball dancing together without knowing it—but the masks they're wearing only cover the eye area of their faces, to say nothing of the fact that they'd spoken to each other at length and thus should have recognized each other's voices. Sort of justified in that they also dressed differently from how they expected each other to dress (Arthur thought Cinderella was going to wear a crummy dress, Cinderella doesn't know Arthur is the prince) and had only met each other once (though they do recognize each other when they next see each other three months later, and Cinderella initially doesn't notice Arthur in prince clothes at first).
Additionally, the only time Cinderella uses her mask as a disguise is when she's near her stepmother and stepsisters. It works, but is justified in that they don't expect her to have such a nice-looking dress. And when the Fairy Godmother encounters Splurge at the dance, she says that she initially didn't recognize him with his mask on. Keep in mind Splurge is a big purple monster and his mask is a Lone Rangers mask.
In an episode of the UK version of Who Wants to Be a Superhero?, after one of Dr. Dark's henchmen steals the secret identity files of their superheroes, they are forced to don disguises and create distractions in an attempt to take them back off him. Most of the heroes' disguises were paper thin and if anything would make them stick out like a sore thumb. Fortunately the henchman was fooled until he saw some of the superheroes taking the files from under his snout.
Invoked in Dad's Army when, on a training exercise, Captain Mainwaring decides to dress some sheep in tin hats to make it look as though they were his men dressed as sheep. Meanwhile Corporal Jones poses as a log using a pantomime costume. It gets funnier.
The same kind of economy casting is used on The Mighty Boosh. But it didn't make Howard and Vince's attempts to masquerade as old ladies in the Bingo Hall seem any less feeble. Howard in particular should really have considered doing something about his moustache...
In LazyTown, no one ever realises the person causing trouble who looks like Robbie Rotten in a silly outfit is, in fact, Robbie Rotten in a silly outfit. This is especially hilarious because his cover is blown at the end of every episode, yet the townspeople will still fall for his paper-thin disguise in the next episode. (And yet, Robbie Rotten himself thinks his disguises are amazingly awesome and calls himself "The Master of Disguise.")
If he actually is fooling everyone, then he's probably on to something.
Taken to the extreme in "Play Day" where his hat falls off and not one person yells "Robbie Rotten!" like they usually do.
Subverted in the episode "Defeeted" where the mayor recognises Robbie straight away, even though the villain is wearing one of his better disguises: a superhero outfit. The characters have fallen for lesser disguises in the past.
It's also worth noting that there are exactly three male adults in the town—the mayor (who's Ambiguously Brown and heavyset), Sportacus (a Caucasian muscular man), and Robbie (who, while Caucasian, is much slenderer than Sportacus), which severely limits the number of people who the Birthday Fairy/manners teacher/scoutmaster/etc. could be...and yet no one ever catches on.
Spoofed in the Nickelodeon series All That, where the local superhero Superdude encounters an impersonator robbing the bank. Said impersonator is a little girl. Despite the fact that Superdude is played by the heavily built African-American teenager Kenan Thompson, and the impersonator is played by the thin Caucasian preteen Amanda Bynes, the Too Dumb to Live townspeople are completely unable to tell the difference between the two, even after Superdude bends a metal bar in a knot and the impersonator simply rips a piece of paper (which the citizens are convinced is a form of Super Strength).
Another recurring sketch, "Cheeseburger Doyle," also spoofed this trope. The main character was a talking cheeseburger with eyes that ran a detective agency—and not a human-sized burger either, but an actual four-inch sandwich puppet. Upon being hired to solve a mystery, Doyle would infiltrate the scene of the crime wearing a disguise, usually a phony mustache or small hat; when questioned if he was a cheeseburger, he'd deny it, making up a generic name ("Oh, no...I'm Al"). After catching the culprit red-handed, he would proceed to dramatically reveal himself: "AHA! I'm not REALLY a construction worker named Al!" After (literally) shaking off the disguise, the suspect would react in over-the-top shock ("CHEESEBURGER DOYLE!"), while others reacted in amazement at Doyle actually being a cheeseburger.
On CSI, in the episode "Living Legend", a series of murders are committed, ostensibly by separate people. All of the killers look amazingly alike (including the one who's supposed to be black and female). All of the killers use names that are obviously cribbed from horror movies. None of the killers try to hide their identities, which don't lead back to any real people. Any viewer with half a brain cell will have figured out by the fifteen-minute mark that all the killers (plus a few other characters) are played by special guest starRoger Daltrey, but it takes the well trained and highly intelligent police until the 48 minute mark to even figure out that any one of the killers is actually using a disguise and fake name, let alone figure out that they're all the same person.
Zigzagged in the Star Trek: The Original Series episode "The Enterprise Incident". Kirk has McCoy use a type of plastic surgery on him so he can infiltrate the Romulan ship and steal the cloaking device technology. While the surgery does give Kirk the features of a Romulan, it's still obviously him. However, because he doesn't come into contact with any Romulans who knows what James T. Kirk looks like, he still succeeds.
On Robin Hood, all the outlaws had to do to render themselves invisible was to put on their hoods. In any given crowd of people, there would always be a little group of people that had their hoods obscuring their faces - this was never considered suspicious.
An especially strange example is when Will Scarlett and Allan-a-Dale put on their hoods after a guard has stormed past and told them to get out of his way.
Funny hats also did the trick, as did a fancy dress for Djaq. Guy of Gisborne stops her as she infiltrates the castle, only for him to give her some orders, thinking she's a serving girl. Just for the record, Djaq was a Saracen woman. I guess Guy sees a lot of them around Nottingham...
The 2005 Canadian series Young Blades was notorious for this. The best example was Jacqueline - a female Musketeer masquerading as a man - who used to conceal her femininity by tying back her (waist-length) hair, assuming a bizarre guttural voice and frowning a lot. In some episodes she sported a highly amusing fake goatee, which only made things worse. And yet no one penetrated her disguise, ever, even when she let her hair down, put on a dress and started pretending to be her own twin sister. It was absurd!
In fact, most of the characters seemed to think that if they just put on a mask that covered their eyes they would be instantly unrecognizable even to their closest friends. They were usually right...
Notably averted in the episode "The Chameleon," where the villain had the ability to shapeshift at will. Though of course, given the good guys' track record for recognizing impostors, an eyepatch and a cigar might have served him just as well.
Also inverted in "The Chameleon," where the Chameleon disguises himself as Jacques, and D'Artagnan claims the disguise was paper thin to him because "Jacques" acted like a man, not like a woman disguised as a man.
Common on Batman, where the citizens of Gotham City are remarkably unobservant when it comes to recognizing Special Guest Villains. On at least two occasions, The Joker is able to successfully impersonate someone else — not by wearing makeup to hide his distinctive features, or even by changing clothes, but by simply wearing a hat (though he did manage a halfway-convincing Texas accent).
Avterted in the film of the series where Penguin disguises himself as the Commodore he and his team have kidnapped. Batman and Robin are not fooled for a minute.
Subverted in Chappelle's Show, when Tyrone Biggums is tricked into an intervention with his friends. One of them, Rhonda, recalls the time that he carjacked her. He tried to hide his identity simply by pulling his red hat over his head like a ski mask, but Rhonda instantly recognized him anyway:
Tyrone: Get out the car! Rhonda: Tyrone, what are you doing? Tyrone: Who's Tyrone? Huh? I don't know Tyrone! Rhonda: No, it's you with your crusty-ass lips. Tyrone: Stop playin', and get out the car! Get out the car! I don't know no Tyrone.
In Tokumei Sentai Go-Busters, villain Enter is made of data and can change his clothes in the blink of an eye, but for some reason never bothers with the rest of the disguise, and maintains his appearance and signature goggles every time.
Subverted in The Big Bang Theory Season 4. Leonard tries to pick up women in an Apple Store by wearing a T-shirt. When that fails, Howard tells him it doesn't work going back with a false moustache.
Inverted in the Drake & Josh episode "The Theater Thug". Because Josh keeps getting attacked because he looks a lot like a wanted criminal, he decides to put on a heavy trenchcoat and hat. Everyone recognized him instantly.
Played with in "Sic Transit Vir", when the Earth Alliance officers discover that the name of the Centauri associated with the death of thousands of Narns is "Abrahamo Lincolni". The Centauri wouldn't necessarily pick up on the name of a historical figure of Earth, but Sheridan and Ivanova (of course) recognize the reference immediately. It turns out that Vir, from his ambassadorial office on Minbar, created the fake noble, and has been using that identity to smuggle those Narns to other worlds, declaring them "dead" so that no Centauri would inquire. Vir is eventually forced to confess the scheme to Londo, but since "Lincolni" himself was never revealed to the Centauri, Ivanova continues using the name in hopes of saving more Narn lives.
Played straight in Alias when Sydney literally uses wrapping paper as a skirt. This and a cheap convenience store wig are enough to fool the valley-girl clique she is attempting to infiltrate.
In the Greg the Bunny episode "The Singing Mailman", when Dottie convinces the others to pretend they like the actor playing the mailman, Greg decides to wear a disguise, which includes a sombrerro, pancho, and mustache. It doesn't seem to fool anyone, but when he removes his mustache, Tardy Turtle reacts with surprise, "Hey! That french man is Greg!"
Usually averted whenever it happens on Sesame Street, when other characters see through the paper-thin disguises. Justified as it is an educational show for children. Some examples include:
In one sketch, Ernie gets a disguise kit and uses it to fool Bert, who is not fooled at all, especially since Ernie left his pirate beard on when he dressed up as Little Red Riding Hood. However, when a wolf shows up, Bert thinks it is Ernie.
In another sketch, Cookie Monster dresses as "The Cookie Bunny", and "corrects" Ernie whenever he refers to Cookie as Cookie Monster.
In a street scene of one episode, Big Bird and Alan bake birdseed cookies for Granny Bird. When Cookie Monster finds out, he dresses as Granny Bird. Big Bird and Alan know that it's Cookie Monster all along but play along with it.
In another episode, Abby thinks Oscar might really be a prince and wants to kiss him, which Oscar wants to avoid. At one point Oscar dons a disguise (Groucho Marx glasses) which doesn't work.
One "Word of the Day" sketch features Jack Black and Elmo defining the word "disguise," so as might be expected, Paper-Thin Disguises came into play. Jack claims to be a "master of disguise," and tries to prove it by putting on various outfits to conceal his identity. The first is a large sombrero and a pair of sunglasses; the second is a rainbow clown wig and...another pair of sunglasses. Elmo instantly sees through both disguises, which makes Jack sad. He leaves, and a few moments later, a Muppet chicken enters. Elmo asks if the chicken has seen Jack Black...three guesses as to who the chicken really is.
In the "Smart Cookies" segments introduced in the 46th season, The Crumb, a villainous chef, is always able to fool Cookie Monster with these kinds of disguises.
In an episode of The Furchester, "Don't Eat the Guest", a talking cookie comes to the hotel, on a day when the hotel is out of cookies. In an attempt to keep Cookie Monster from eating the guest, the staff puts a fake mustache on him so Cookie won't know that he's a cookie. Sort of works, though Cookie Monster does say that he thought it was a cookie at first ("But whoever heard of cookie with mustache?").
An episode of Adventures in Wonderland, titled "The Queen Who Came in from the Cold", featured the Queen of Hearts—a heavyset black woman with a fondness for wearing all-red outfits—upset about receiving a number of anonymous letters complaining about her newest taxes. To find out who the letter writers are, she assumes a disguise—a crimson dress, her hair partially over her face, and a large red hat—and speaks in a half-whisper, which makes her look remarkably like...a heavyset black woman with a fondness for wearing all-red outfits. It fools everyone but the Cheshire Cat—and the characters interact with the Queen on a daily basis! What makes it even funnier is that there are no other women, African-American or otherwise, in Wonderland, and yet everyone is completely unable to recognize her.
The show also occasionally spoofed this idea with the Mad Hatter. In "Christmas in Wonderland," the gang meets to plan a holiday surprise for the Queen of Hearts. Tweedledee points out that, since the gift is a surprise, it should be a secret meeting—if the Queen spots them, the plan will be ruined. The Hatter announces "Only if she recognized us!", and provides everyone, including preteen Alice, with the same disguise—a large white Santa Claus beard.
Deliberately invoked and subverted in The Cosby Show episode "Theo and the Real World." As the title suggests, the episode features Theo boasting that he'll be extremely successful as an adult in the "real world." To test this theory, the rest of the family convert their brownstone into the "Real World Apartments," and pose as various people that Theo might experience while trying to rent an apartment, find a job, buy furniture, and get a bank loan. They change roles by assuming simple costumes and props—Cliff's "landlord" outfit, for instance, is simply turning a baseball cap backwards and putting a cigar into his mouth. The subversion comes in as the family isn't trying to trick Theo; the disguises are simply to indicate that they're different individuals, like costumes in a play.
In the Supernatural episode "What Is and What Should Never Be" (S02, Ep20), Dean believes changing the car's license plate and getting new credit cards should be a sufficient disguise. They continue to drive a 1967 Impala and do not alter their appearance, despite having recently escaped from prison and having arrest warrants in at least five states.
In Charmed, the sisters fake their deaths at the end of season 7. In season 8 they pretend to be their own "cousins" and continue living in the same house, raising Piper and Leo's kids. They do change their appearance using glamors (though they also change the glamor multiple times). At one point Piper's glamored appearance turns out to have been copied from someone wrongfully accused of murder, and she's imprisoned. This doesn't seem to raise any questions about why the other two were letting this woman live there, pretending to be related to them. Muggles get a pass for not guessing the truth, but this subterfuge should have fooled demons for about half a second.
Taken Up to Eleven in the Studio C sketch "Death Bed Repentance", where the audience doesn't even realize that Jeremy is even wearing a disguise until he takes off the fake mustache and wig, revealing his identical mustache and hair, to prove that he is actually Jose Delgado.
Logan tries to pass for Chase in Zoey 101 while trying to join the secret school society. Nobody is fooled by his Afro wig.
In You're The Worst, whenever Jimmy wants to be incognito, he wears a hat and a fake mustache that make him look like Mario
Happens in Sherlock. In "The Empty Hearse", Sherlock disguises himself as a French waiter by stealing a black bowtie, horn-rimmed glasses, scribbling on a fake mustache, and talking in a French accent when attempting to reveal that he's still alive to John. And John is so distracted that it still takes him a few minutes to realize that he's been talking to Sherlock.
While Mad TV's Smith Comma John looks completely human, his disguise is rendered paper thin by his loudly announcing to anyone that will listen that he's not an alien. For example, he can use a 3-way light bulb, and sit near a dog. Could an alien do that? Apparently not.