From "Clark Kenting" Real Life Tab on tvtropes.org :
Jay Leno and Jimmy Kimmell pulled this off by disguising themselves as reporters.
"Creator/folieadonteven" was a vicitm of this, his friend Ginny had made a parody account on instagram, playing a chraracter called "Juan." "Juan' was Ginny with a mustache and a beanie, yet Kax was 100% convinced that he had two seperate friends named Ginny and Juan, and even though literally ""everyone else had known since she made the account"", Kax did not even think about the concept until Ginny's best friend told him. His reaction video is priceless.
Jimmy Kimmell's cousin once snuck into Super Bowl media day simply by dressing up in the uniform of Carolina Panthers Kicker John Kasay. It worked, because of all the hundreds of reporters who covered the event, none actually knew what Kasay looked like.
A rumor spread by his detractors says that because of the controversy surrounding his election, Abraham Lincoln dressed up as an old woman for his own safety to get through Baltimore on the way to his inauguration. Maryland was a pro-slavery state where Lincoln was incredibly unpopular, and there were reliable reports warning of an assassination plot. Since he was 6'4", he had to hunch over to pull this off. In reality he did wear a slouch hat and overcoat in a failed attempt to appear less obvious, but he did not disguise himself as a woman. (In a Brick Joke, at the end of the war Northern supporters falsely claimed that Jefferson Davis was captured while disguised as a woman).
Most of Sacha Baron Cohen's characters are this. Like Borat, which consists of a mustache and accent.
Tom Cruise prepared for his role in Collateral by taking a job as a UPS courier, which he worked for weeks while secretly filming himself. The video shows Cruise interacting with customers, walking around in broad daylight and even having protracted conversations with people on his lunch break, and going totally unrecognised because he was wearing sunglasses and a hat.
Harold Lloyd, an inspiration for Clark Kent, found that if he took off the stage glasses of his most famous film character, no one recognized him.
Charlie Chaplin without his moustache and Nice Hat.
Reportedly, he also once lost a Chaplin look-alike contest.
That's because he showed up as himself, i.e. the film actor Charles Chaplin, without the costume or the mustache (he never actually grew such a mustache, it was always a stick-on). Everybody knew who he was and had a nice laugh.
Another version that explains is that he got third because, while the mannerisms and looks were perfect, he didn't have a costume. (The contest was to be his Tramp Character. He was wearing his street clothes.)
A documentary on spying had a section regarding disguises and how they're used, with a former CIA specialist explaining how simple disguises can work wonders if you play on observers' expectations. As a demonstration they had people assigned to trail a blonde woman dressed in jeans, a hoodie, boots and a ballcap, carrying a backpack. The woman faked drinking a lot of water and thus had a reason to duck into a bar to use the bathroom. While they were intently observing the bathroom and the back alley door, they never noticed the brunette wearing a little black dress, heels, and carrying a small purse who strolled out the front door on the arm of the man who'd been waiting for her.
An inversion occurs with pornstar Eva Angelina in that her glasses have become so synonymous to her general appearance that she's gone to conventions without them and wasn't recognized at all.
Comedian Groucho Marx painted on his famous mustache with grease paint for most of his career. He was surprised to find a large crowd of fans who had gathered to see him at a train station completely ignored him when he got off the train. Realizing what had happened, he ducked into his car and smeared on a grease paint mustache, and was instantly recognized. There is even a story (probably apocryphal) about Groucho house-sitting for a friend in Beverly Hills. He was taking advantage of the swimming pool and had the cops called on him by the neighbors. No one would believe he was Groucho Marx without his mustache. (He actually grew a mustache later in life, a bit before he started hosting You Bet Your Life.)
Reportedly, Marilyn Monroe would employ this with a curly black wig, a pair of sunglasses and some loose-fitting clothes. She was also apparently very good at changing her body language in public, to the point where she was able to walk completely ignored in a crowd until she fluffed up her hair and struck a pose, and was instantly swarmed.
"Do you want to see her?"
Many decades ago, photographs were rare and hard to produce, and people with the artistic skill to do a composite sketch were scattered much further apart. Thus a fugitive could reasonably move to another place without notice. The Wanted Poster was less effective than it is usually played to be; criminals on the run were often chased by former acquaintances, the only people who could recognize them.
Stewart Copeland in the years 1978 - 1980; a link.
Aviator Charles Lindbergh actually used the alias of Careu Kent when visiting his secret second family in Germany.
Shakira went unnoticed in public for a couple of months by wearing modest clothing, going by her middle name and wearing a baseball cap.
The use of a fake distinguishing feature such as a scar can make people focus on the scar so much they don't notice any other real details.
Eric Morecambe, at one time half of the most famous comedy double act in Britain, used to get by in public by taking his trademark glasses off and affecting a limp. His son has stated that this worked so well he wouldn't even get recognized by people sitting next to him on trains or planes.
Although it's possible many people did notice, but were too polite to blurt out "Hey! You look just like Eric Morecambe!" to a complete stranger who was likely well aware of the fact and heartily sick of his friends and relations making jokes about it.
Many models can have relatively normal lives by simply wearing minimal or no makeup, pulling their hair back into a simple hairstyle like a ponytail, and wearing some reasonably conservative clothing. Since most people see them professionally made up, and often in photoshopped images, it's easy for them to be less noticeable. There are models who've walked into their agency's offices, with pictures of themselves plastered all over the walls, and not been recognized by the staff because they've been in casual clothing and not posing.
For nude models and porn actresses, often merely wearing clothes suffices to make them unrecognizable.
Jewel went onstage at a Karaoke bar as 'Karen', wearing a wig, glasses, and false nose, and was unrecognized. (A few people even called her 'homely'.) She sang a few of her own songs, to acclaim from the crowd. She then stripped off the disguise and went back in as herself and sang a few. No one made the connection. Admittedly, it was dimly lit.
Murderer Ted Bundy was able to walk around in broad daylight for days while a wanted fugitive whose face was plastered all over TV. The only attempt he made at a disguise was drawing a mole on his face with a marker.
Anybody who's ever worn glasses for years and then suddenly switched to contacts (or vice versa) knows that you can look like "a whole different person." Glasses come with a very specific set of cultural stereotypes, which are completely destroyed when you get rid of them.
Same thing with, say, wearing a substantial amount of makeup regularly and then suddenly appearing without it.
Anyone who loses a large amount of weight quickly (whether by diet or illness) knows the feeling of going completely unrecognised by people who knew the old overweight persona. Weight loss changes everything: body shape, posture, manner of walking, and in other subtle ways.
Or shaving off your facial hair.
Or shaving one's head or changing one's hair color substantially.
PokerStars once challenged tennis star Rafael Nadal to bluff people into believing that he wasn't Rafa with only a pair of glasses and a golf receptionist's uniform as a disguise. He didn't succeed.
This is the essence of other tropes like Clipboard of Authority. Attitude and body language matter as much as clothing or make-up. If you act like your role, then people assume you really are your role. Discussed further in articles like "How to Sneak Around."
This is more intricate than most examples of this trope, but scientists have developed a wearable device that prevents facial recognition cameras from recognizing the wearer. It's a pair of glasses.
One interviewer accompanied Mel Gibson to the DMV, with only a baseball cap as a disguise. He then watched Gibson visibly "turn off the charm" and become so inconspicuous that only the ID photographer noticed a vague similarity.
While not one of the Tropes Examined By The Myth Busters on the show, they were asked to test this out at their San Diego Comic Con 2012 panel, which they actually did. Here were the results:
Tory went with the glasses disguise and failed miserably.
Kari noted that wearing a full costume makes a person a little too suspicious, as if you're trying to hide. Adam, a noted cosplayer who made a game of playing hide and seek by wearing full costumes at each SDCC, found this out the hard way when someone recognized him straight after just donning his cosplay and exiting an elevator.
However, Kari then noted that wearing a cap was sufficient enough to fool everyone (she even fooled Grant and other friends when she walked the floor wearing one).
Adam himself told on the show that he is more recognized on the street when he is together with Jamie, because while people can recognize his features, it's Jamie's trademark dressing style that takes the spotlight.
"I might be that guy from that show, but he is definitely that guy from that show."
Tyra Banks once did this live and in person on an episode of the Today show. Without makeup or hair styling, while walking with a slump and wearing a pair of glasses, she went into the crowd outside the Today set's window as a "production assistant" to ask people about their opinions about supermodels and Tyra Banks in particular. After a couple of minutes of absolutely no one realizing it was her, Banks pulled her hair back, straightened her posture, took the glasses off and suddenly ''became" Tyra Banks, Supermodel. The crowd loved it.
Superman goes shopping.
Jennifer Grey, star of Dirty Dancing et al, accidentally destroyed her career by getting her nose done. Afterwards, even friends didn't recognize her.
Bryan Cranston once successfully infiltrated the San Francisco Comic Con by cosplaying as his Breaking Bad character, Walter White. No one expected the "real" Walter White to be wandering around the convention like any other con-goer, and so they assumed he was just a look-alike in a costume.
Perhaps more forgivably, Gene Simmons once allegedly attended a KISS concert without his makeup, and nobody looked twice at him.
The whole concept of wearing masks can often fall into this trope, specifically masks that only cover a small portion of the face surrounding the eyes. If the person has any distinguishing facial features at all, such masks are useless at hiding a person's identity. Or so one would think; such masks (think like the ones Catwoman or the Riddler wears in the 1960s Batman TV show) have been successfully used to obscure people's identities at everything from masquerade balls and swinger's parties to bank robberies, even though by rights they shouldn't work. They still work today even though digital technology allows anyone with a computer and Photoshop the ability to erase the mask from any images of a person's face.
Walt Disney would anonymously spend an afternoon every week at Disneyland, making sure that everything was working smoothly. Despite hosting a very popular Tv-show, all it took was an pair of sunglasses and an Hawaiian shirt to make sure that nobody recognized him.
While filming House of Wax in Australia, Paris Hilton had to wear a brunette wig if she went out in public to do her exercises. She wasn't recognized if the making of TV spin-off is to be believed.
Paris was also part of a hidden camera show that explored this trope. Named I Get That A Lot, it would feature various celebrities in public jobs. If a customer noted their 'resemblance' to themselves, they would say "I get that a lot". Paris pretended to be a gas station attendant.
Hayley Atwell has twice been in places where movies with her in them are playing. She wasn't recognized either time, and all it took was a pair of glasses.
According to Hulk Hogan's autobiography, he was able to go out in public wearing a coat, hat, and glasses and not have anyone recognize him until he took them off.
Taken Up to Eleven when Henry Cavill wandered around Times Square and wasn't recognized, despite there being large ads for Batman v Superman: Dawn of Justice in the area and the fact that he was wearing a Superman shirt.
Without the trademark white-blonde wig she uses to play Daenerys Targaryen, brunette Emilia Clarke hardly ever gets recognized in the street. Even when she is out with other members of the cast.