Hugh Mann

Zapp Brannigan: We can't be too careful with these codes [to Earth's automated defenses]. Rumor has it a double agent may be aboard this very ship. You, ensign, what's your name?
Decapodian in a Paper-Thin Disguise: Hugh Mann, sir!
Zapp: Hugh Mann? Now that's a name I can trust. Run down to the central battle computer and enter these codes. Chop, chop!
Kif: Um, sir? There's something about that ensign that's--
Zapp: You're damn right there is! That strapping young lad's gunning for your job. And he just might get it.

—Futurama

Someone has gotten duplicated/taken over/impersonated by something not human, and the duplicate is trying to pass as a main character. But they do a terrible job of it; acting in an erratic manner, forgetting names, walking stiffly, and talking in an odd dialect. They might as well call themselves "Hugh Mann" and walk around with a name-tag reading "I'm Most Definitely Not A Space Alien" - it would make for about as convincing a disguise.

Luckily for them, nobody notices at all. Or at least nobody anyone will listen to. Sometimes, it helps that the character that's being impersonated normally acts this way.

See also Clark Kenting and Paper-Thin Disguise. Compare Louis Cypher. Not to be confused with Funday Pawpet Show character Hugh Manatee.

Examples of Hugh Mann include:

Comic Books

In an issue of Impulse, Bart has to hide the fact that his cousin Jenni is from the future, so he teaches her English with the help of books like "See Spot Run". When introduced to his friends, Jenni's first attempt at conversing with them is to ask if they've Seen Spot Run.

Film

In Tim Burton's Mars Attacks!!, a Martian disguises his... her... itself(?) as a voluptuous babe to catch the attention of a horndog White House staffer (the better to gain access to the President). She walks, talks, and does everything "strangely" but he doesn't notice until she bites off his finger!!
The Lost Skeleton of Cadavra:

Kro-Bar: My wife sometimes forgets that she is not a space alien.
Kro-Bar: Aliens? Us? Is this one of your Earth jokes?

Edgar, in the first Men in Black movie.
- In-Universe, Dennis Rodman is this. "It's not much of a disguise". And according to the sequel, Michael Jackson.
In The Human Duplicators, a detective gets duplicated (Surprise!) and the duplicate reports back to the original's superiors to throw them off the case. Despite his random pauses and stiff movement, they don't suspect a thing.
Absolutely ruthlessly parodied in Monsters vs. Aliens where the aliens can tell that the ancient fishman is not one of them (although they believe him to merely be a defective clone) but cannot identify a one-eyed slime monster or a six foot cockroach as not being one of them. The disguise that leads them to believe that they are mere clones? Simply their ill-fitting uniforms.
In It Came from Outer Space, altruistic aliens that accidentally crashed on Earth entrust a local science-fiction writer with holding off local scrutiny while they temporarily hold a number of local townspeople hostage and imitate their bodies to be able to move about freely in town so they can get their ship fixed. Needless to say, they all talk in straight-faced monotone and walk rather awkwardly.
The Skeleton Key ends this way, although at least one person seems to suspect something might be wrong.
The Strangers from Dark City. By extension the whole environment they constructed .
In the second Cats and Dogs film, a cat (masquerading as his owner) over an intercom gives his last name as "Not-A-Cat". The humans believe him!
Deconstructed in Hellboy: II The Golden Army. Princess Nuala, when first meeting Abe Sapien, thinks that his name is an obvious alias and that he's one of Nuada's spies, so she reads his mind to find out his real identity, only to learn that "Abe Sapien" is actually his name.

Literature

The Hitchhiker's Guide to the Galaxy has a few borderline cases. Ford Prefect and Zaphod Beeblebrox both visit Earth without attracting too much attention, despite the former's badly chosen fake name and Zaphod not even trying to hide he's from space; of course, they're both basically human-looking, with just a few subtle (or not; see below) oddities. Later on, the mice offer to replace Arthur's brain with a computer, and Zaphod jokingly suggests that it would only need to be able to say "What?", "I don't understand" and "Where's the tea?" and no one would notice any difference.
- It doesn't exactly help that Arthur blurts out "What?" on this suggestion.
- In the game (and in the book Mostly Harmless), it is revealed that the two-headed Zaphod went to a costume party on Earth dressed as a pirate. He put a birdcage over the second head and covered it with a cloth. The head in the cage said "Pretty Polly" every now and again.
A more serious example would be H.P. Lovecraft's The Shadow Out of Time, in which the main character is assumed to be mentally ill during the period when a Yithian occupied his body.
Mostly averted by R. Daneel Olivaw of the Robot/Empire/Foundation series by Isaac Asimov, but every now and then the ten-thousand-year-old robot gets the urge to call himself something like "Chetter Hummin" ("Cheater Human") for a while. This is probably a way to evade the psychological cost of lying to humans, which is an indirect violation of the Robotic Laws.
Several times throughout Animorphs, though never involving the Yeerks, who have already an access to their own host's knowledge and personality. In one memorable mess, Jake is taken over by one (that gets access to his memories) and it plays the part almost perfectly. When his own teammates realize this, they tie him up in the woods until that alien dies of hunger- then had another alien (who doesn't have access to his memories) play the role of Jake badly, while all this is going on... To his own family's shock.
- This is actually something of a running gag for Ax whenever he's in his human form, particularly about food. This boy enjoys eating cigarette butts and other strange stuff...
  - And Cinnamon buns (who would blame him? Cinnabons).
- At one point, Ax gets asked about where he's from? After his first response ("I am from the Republic of Ivory Coast") doesn't work, Ax just lists off a bunch of World Almanac countries- until finally hearing a suggestion of Canada... At which Ax now promptly notes "I am from Canada. I am Canadese." as his reply.
- Fortunately, they eventually get access to the Chee, who at least understand not to eat cigarette butts...
  - They did however, cleaned Marco's room with their pleasure, which is probably just as weird for him. The act irritates Marco to no end, at any rate...
  - And almost blew their cover, as the now very clean room now confused the hell out of Marco's father!
In the Mark Clifton short story What Have I Done?, an employment agent meets an alien who asks him to help the alien invaders with their disguises. (The agent has a superhuman ability to read people, and is the only person so far who's seen through the Hugh Mann act.) He defeats the invasion by helping them to appear as the most perfect, noble humans ever - so that real humans will destroy them out of envy.

Live Action TV

In the Doctor Who episode called "Rose", Mickey is sucked into a trash can and replaced by an Auton. Despite the fact that he looks like a mannequin, his hair is an obvious wig, his skin is waxy, he can't drive, and he suddenly stammers in a skipping-record sort of way, Rose doesn't realize what's going on until The Doctor shoots a champagne cork through his head. Sure, she's never been very observant when it comes to Mickey, but come on...
- This varies by scene. In the scene in the car, he is very obviously a mannequin. In the scene in the restaurant, he's just got a sheen to his skin and the funny talking.
- Subverted in another episode of Doctor Who, "New Earth." Cassandra now possesses Rose, and the Doctor pretends not to notice till anything becomes sufficiently dramatic.
- Another subversion: In "Human Nature"/"The Family of Blood", after one of the characters becomes possessed, Martha notices something off about her, and she confirms this by asking whether she'd like jam and sardines in her tea. "I like the sound of that."
Reversed and subverted in an episode of Stargate SG-1. Reversed, in that it's a human, Daniel Jackson in this case, trying to pass for a Goa'uld—hey, at least he speaks the language!--and subverted in that the name he gives, "The Great and Powerful Oz," doesn't fool anybody.
- Also played straight when Sam is taken over by a Tok'ra. She acts rather odd, but no one seems to notice anything until she starts dialing up the gate. In another episode, Colonel O'Neill is duplicated by a crystal entity and everyone, even his ex-wife, thinks the entity is him even though he speaks very haltingly and suddenly acts like he's once again depressed about his son's pre-show pre-movie death. Another reversed/subversion in another episode, O'Neill pretends to be a Goa'uld (although all he knows is "Jaffa Kree!") but the Goa'uld he's trying to bluff don't really buy it.
  - O'Neill thought it might work because the last time the people he was trying to bluff saw him, he was about to be implanted with a Goa'uld symbiote. Unfortunately for him, he didn't know that Goa'uld (as well as former Goa'uld hosts) can sense the presence or absence of a symbiote.
- The O'Neill duplicate episode came fairly early in the series, and the team didn't know each other all that well yet; Sam didn't even know about O'Neill's family tragedy. O'Neill's ex-wife just assumed he finally wanted to talk about their relationship and their son's death—she noticed his odd behavior, but assumed it was caused by psychological trauma. Since she was a Muggles, there was no reason for her to suspect that "space alien duplication" was a valid explanation.
- Jackson pretending to be a bounty hunter: "My name is... Olo. Hans... Olo."
- Lampshaded in "Off the Grid" when Daniel, Cam, and Sam are all arguing over who would make the most convincing drug dealer for their meet with the bad guys and Teal'c says they're all equally unlikely. Subverted when Mitchell's attempts at posing as said drug dealer backfire off screen and the audience just sees the team running for their lives.
In the comedy soap opera Soap, Burt was replaced by a look-alike alien Burt. Though alien Burt acted very oddly and was sex-crazed, only his wife Mary was really concerned, because the real Burt was pretty odd himself.
In Buffy the Vampire Slayer, Buffy's close friends took the Buffy-bot for the real thing, chalking its odd behavior up to the fact that she had recently lost her mother. Buffy was nevertheless entirely unimpressed with her friends after this was discovered, probably because the robot was still practically wearing a t-shirt reading "Hello, I am a Robotic Impersonator" the entire episode.
- Anya seemed to like the robot better than the regular Buffy, particularly after its greeting of, "Hello, Anya. How is your money?" Anya replies with a happy, "Fine! Thank you!" apparently glad that someone now cares about the money as much as she does.
- We also have all of the demons at Xander and Anya's wedding, and Clem at Buffy's birthday party.
  - And Anya herself, when she's trying to keep the Watcher's Council from finding out she's an ex-demon:

ANYA: Anya Christina Emanuella Jenkins, twenty years old. Born on the fourth of July, and don't think there weren't jokes about that my whole life, mister, 'cause there were. Who's our little patriot? they'd say, when I was younger, and therefore smaller and shorter than I am now.

Done hilariously in an episode of Mad TV, where throughout the episode, segments were aired for "Smith Comma John, Human Being for President", in which the candidate demonstrates his human American nature with statements like "I am sitting next to fire. Willingly." and introducing his wife: a golden retriever. The capper is when he partakes in the all-American activity of eating corn dogs, first sticking his hand into a deep fryer to retrieve one, and then "eating" it via the magic of visual effects: the camera stops for a moment, a bite is missing, and he pretends to be chewing, before going for another "bite". Sooo not an alien.
In Smallville, after being a Human Popsicle for months, Clark Kent is enraged when he returns and finds that Bizarro (this version looks exactly like Clark, except when sunlight falls on him) had stolen his identity, and no one except Chloe noticed. Chloe had no choice but to stay silent, as Bizarro would have killed her if he found out that she knew. Clark would have been fine with it if Lana had also been playing along, but she was completely fooled and had sex with Bizarro several times.
A That Mitchell and Webb Look sketch parodying Battlestar Galactica has Bob, the infiltrating robot. Who has a bucket for a head, and uses his clearly mechanical voice to say things like "Does not compute."
In The Secret Circle Melissa is possessed by a demon. Turns out, demons aren't very good actors. Apart from general weird and out of character behavior, when frustrated she broke into Evil Sounds Deep. Unusually for this trope their friend screaming at them in demon voice because they expressed reservations about her creepy plan was noticed, although the real giveaway was when the demonic snake crawled across her forehead under the skin.
In Zardip Zap, a series of fitness and health information videos for children, the eponymous character is an alien sent by his leaders to re-learn the secret to taking care of one's body. masquerades as a child named Zardip Pacific in order to gain information. He pulls it off rather well aside from not knowing what the organs in his own body are.

Music

The Duras Sisters' eponymous track on "Masquerading as Human" describes something that's doing just that, and finding just how easy it is to do so, even when they do things like order steak with marmalade and have a deadbolt on their closet door.
Likewise, filker Karen Lindsey and her song "Nobody Knows I'm Really an Alien." The marooned alien cook is having a great time of it on Earth. He lives in a hippie commune (where the residents have had so many drugs they don't notice), goes to sci-fi conventions (where his looks are mistaken for a great costume), and even gets bit parts in Hollywood films (where again, no one seems to notice). It's only when he goes on a talk show to "set the record straight" that the MiB patrol shows up to cart him off.

Theater

In Dark of the Moon, the protagonist, a witch, pretends to be a human. When asked what his name is, he says, "John... Human!" Cue bewildered remarks from the other characters.

Video Games

If you hide for some period in Halo, Grunts may occasionally respond with: "It's okay to come out now, this is Sergeant... Smitherson! Yeah..." Occasionally they'll play it straighter and reply as "Sergeant Humanoid."
In Mechquest, you'll encounter an alien NPC named Hugh Munn. Hugh did play his role as a human rather well- if not for those tacky implants on his head and blue skin...
In Rift, there are a group of...odd people that, should you greet them, will say things like: "Hello, fellow air-breather!" They also sell strange items.
Inverted in Sam and Max Hit The Road. At one point in the game, the eponymous duo put on a paper-thin Bigfoot disguise to sneak into a convention. Also subverted in that the bouncer makes it clear that he knows they're in disguise, and he's only letting them in because they did him a favor earlier. Played straight with the rest of the bigfoots, however, who don't see anything out of the ordinary, even when the bigfoot's navel starts talking.
In Final Fantasy VII, the team sneaks aboard a Shinra ship disguised as Shinra soldiers. Red XIII, a red wolf-like creature, clearly has trouble standing on two legs, and doesn't bother to cover his tail. Naturally, their cover is not blown. (That said, no real Shinra soldiers are ever seen speaking to him, and given his familiarity with humans it's unlikely he'd say something too ridiculous even if they did.)
One of the new classes in Super Monday Night Combat is Karl, a reconnaissance cyborg developed to infiltrate the society of the lawless Outlanders. Uniquely for this trope, Karl seems to completely buy into the idea that he is human. In-game, he'll often talk about getting goosebumps, needing a drink, or being due for a haircut. His bio mentions that he has an extreme hatred of robots and that his locker room outbursts are "just a little too perfect."
In Lego Star Wars, your characters can don Stormtrooper helmets to get into restricted areas. Chewbacca is so big that he can only wear his as a hat on top of his head. Not to mention he is seven feet tall and covered in fur. The disguise still works.
Asheron's Call bad guys the Virindi have a shaky grasp of human psychology, being an otherdimensional Hive Mind of energy beings - actually, they have a shaky grasp of the material world, period. Their best attempt at making human infiltrators, the Simulacra, finally got the physical part right, but they still address people they meet as "fellow human" and talk with unnatural Sesquipedalian Loquaciousness.
Invoked by the game Human Simulator, in which you play a hapless android named "Hugh Mann", attempting to fit in with all the non-androids around him.

Web Comics

Broodax of Penny Arcade.
Parodied in this Legostar Galactica strip.
Also parodied in the Sluggy Freelance "Stick Figures IIIIIN SPAAAAAACE!!!" arc, where the android infiltrator is the only stick figure to have a square head, and his alias is "Ensign Bandroid".
Often seen in El Goonish Shive. Notably here, and handwaved here. (Note that just about all of the 'aliens' seen in EGS are Earth-born Uryuoms, and the technology exists to give them completely human forms.)
This VG Cats strip combines a (rather squicky) example with a case of Most Definitely Not a Villain.
A Casey and Andy comic had a small, one eyed green alien trying to pass of as a human by wearing a yellow smiley-face mask. Casey comments on how stupid the disguise is. The alien comments on how stupid humans are for having their most vulnerable part so exposed. Via a practical demonstration, naturally.
When Corlis (dragon) and Moppy (cat) from Dragon Tails attempt to board a plane with a Paper-Thin Disguise, Corlis delivers "I am Bob Human, and this is my friend Bill Human. We are both human."
Taken to its flimsiest extreme in this Buttersafe strip.
Warmech of Eight Bit Theater. When he pretended to be a human, he wears a fake mustache which he grew on his human lip between acts of defecation. He actually fooled the other warriors with his disguise.

Western Animation

The Brain Slugs from Futurama play it for laughs. The slugs fool no one, but the other characters treat the infected characters like Bunny Ears Lawyers.
- They have to, lest the slug becomes suspicious, and, in Leela's words, "assimilates" them.
- Names the trope in the episode "A Taste of Freedom".
"Bill Cosby" from the Trapper Keeper episode on South Park is a Terminator-esque operative from the future who takes a contemporary name.

Oh, I see. Alright, I'll pay 100 geliga stones -- uh, I mean, hu-mon dollars! -- eugh, I mean dollars!

The Simpsons:
- In a Treehouse of Horror episode, where Kang and Kodos attempt to sabotage the 1996 American presidential election by assuming the identities of Bill Clinton and Bob Dole. In one campaign speech, Kang (as Clinton) monotonously intones "I am Clin-Ton! As overlord, all will kneel trembling before me, and obey my brutal commands!" before crossing his arms over his chest and shouting "End communication!" His staffers attribute the behavior to an "over-tight necktie".

Marge: That's slick Willy for you, always with the smooth talk.

- In another episode, Homer is kidnapped and replaced by a lookalike who speaks with a German accent, has no understanding of Homer's personality, and explains the sense that there's something different about him by stating "I am a new tie wearing." Subverted; Marge sees through it immediately, but she still decides to go along with it after he promises her sex.
In one episode of The Flintstones, The Great Gazoo creates a duplicate of Fred. The duplicate can only utter the words "Yes yes yes", separated by one second pauses. Despite this, absolutely no one notices the difference.
- There's a second episode in which aliens produce multiple Fred clones. They can say nothing more than "Yabba. Dabba. Doo." And almost no one notices.
Star Wars: The Clone Wars had an interesting example in the episode Rookies. Commando droids pretended to be clones, but tended to speak with sort of a stilted rhythm, gesticulated wildly...and ultimately gave themselves away with "Roger, roger.". Hilariously inverted when Captain Rex (in the same episode) re-takes the base by ENDING his sentences with "Roger, roger" and fooling the droids into thinking he's one of them. In addition, he was wearing his own custom armor, which the droids never seen to have noticed.
Frequently used heroically by Scooby-Doo, who seems to get away with impersonating the bad guys' own human and/or monstrously-disguised henchmen with ease, despite being 1) a terrible actor, 2) impaired by a speech impediment, and 3) a freakin' Great Dane.
In Aqua Teen Hunger Force, a clone of Master Shake is created and sent by the Plutonians to impersonate him, but is horribly deformed, calls himself "Major Shake", and loves to give blood (whereas Master Shake thinks donating blood is part of a pyramid scheme run by Dracula and his night slaves). Frylock pretty much immediately figures out that "Major Shake" isn't really Shake, and hilarity ensues.
- The hilarious part is that "Major Shake" is a seemingly normal, decent, average person, whereas Master Shake is a sociopathic obnoxious Jerkass. Major Shake also looks like a slightly melted version of Master Shake, wearing red high heeled shoes, and with a jambox melted into his side.
  - And he doesn't actually have any mission or agenda, and is rather confused about what the heck the Plutonians are hoping to accomplish.
In an episode of The Tick (animation), Arthur was cloned by their alien neighbor. The clone was greenish and could only say "I Arthur", yet he fooled the Tick (not that it's very difficult with him). When he found both the original and the clone, he told them to say something only the REAL Arthur would know. Arthur delivered a lengthy anecdote about a personal incident they had once, which convinced the Tick... while the clone said "I Arthur", which ALSO convinced the Tick, since he couldn't find any fault in the statement.
In the SpongeBob SquarePants episode "Imitation Krabs", Plankton tries to infiltrate the Krusty Krab inside a Mr. Krabs robot. The robot is clearly made of sheets of metal with visible rivets, runs on wheels, has a sputtering exhaust in the back, and talks in Robo Speak, in Plankton's voice no less. SpongeBob, of course, is completely fooled. Squidward sees through the ruse immediately, but plays along after robot Krabs give him the day off.
In the episode "Prime Problem" of the original Transformers cartoon, Megatron creates a clone of Optimus Prime and operates it remotely. The Autobots can't tell the difference between the clone and the original, despite the fact that Megatron calls Ironhide "Bumblebee" and can't operate Teletran 1. Amongst the methods used to try to tell the two Optimus apart is a race. Yes, a race.
- To make the name mix-up even more ridiculous... Ironhide is one of the highest ranking officers. Bumblebee is not an officer and is a member of the Spec Ops team (either a spy or assassin, depending on source material). Any leader worth his salt should know his enemy's highest ranking officers, especially when he's been fighting them for millions of years!
- Another Transformers example, this time from Transformers Animated. The supposed traitor Wasp traveled to Earth to get his revenge on Bumblebee, by swapping places with him. The team aren't suspicious at all when "Bumblebee" starts talking weird and has no idea what happened earlier in the show, despite the fact that they were trying to convince Sentinel that the real traitor was still on Cybertron! At least later in the show, "Wasp" is able to prove that he's the real Bumblebee by telling Bulkhead something that only the two of them know from their days in Autobot Boot Camp. And then Bulkhead convinces the rest of them to go with a test for which is the real Bumblebee: playing against each other on a video game. Justified in that Bumblebee is a video game junkie and quite good at it, and Wasp hasn't had the time to hone his skills at it.
Zim from Invader Zim is... not a very convincing human, to say the least. Luckily, Earth is filled with morons/people who don't care who won't listen to Dib.
- And Dib's sister, who is just Genre Savvy to see that Zim is far too incompetent to have much chance of success and so doesn't give a damn.
Inverted on Galaxy Rangers where humans on Tortuna usually have to pass themselves off as some other alien species like Lumwumps or Zanguils. Justified in that any human caught on Tortuna gets sent to the Queen and their souls ripped out...
In Archer, Barry Dillon's fake Israeli passport reads "Sy Berg", after he is rebuilt as a cyborg. He also doesn't act very naturally when going through customs, leaving them with "Shalom, or whatever it is we say."