Billy Jack: I'm gonna take this right foot, and I'm gonna whop you on that side of your face... and you wanna know something? There's not a damn thing you're gonna be able to do about it. Mr. Posner:(sarcastically) Really. Billy Jack: (nodding) Really. (does exactly what he promised)
Tengen Toppa Gurren Lagann: Because Simon is a skinny young kid, no one (except Kamina) ever respects him as much as they respected his muscular older bro, even though Simon is and always has been infinitely more powerful than Kamina.
Which makes at least one major aversion rather notable. When Luffy learns that his brother is on death row, he resolves to rescue him, despite knowing that said brother is in the pirate crew of Whitebeard, who is absolutely guaranteed to make a move to rescue him already, and is far better equipped to do so. Everyone tells Luffy that he'll be in completely over his head if he tries to butt in, and they're absolutely right. Luffy spends the entire battle getting repeatedly curbstomped by pretty much every antagonistic named character he encounters, needing to get bailed out by either a member of Whitebeard's crew, or one of the allies he made in Impel Down. In his defense, though, he does manage to pull a few crucial moves, and is the one who eventually rescues Ace. Briefly.
Donquixote Doflamingo is a stand-out aversion, as he has actually observed other people underestimating Luffy and his crew many times in the past and suffer humiliating losses. His approach against them is to finish them off as quickly as possible.
That said, once he gets the upper hand, he starts falling prey to this. Law even pointed this out by asking him if he's going to be one of the countless many that would come to regret underestimating the Straw Hat Pirates.
Sugar lampshades this to the dwarves
In Darker than Black: Ryuusei no Gemini, Section 3 underestimates Hei after they Depower him, and Genma thinks that he's "just a gloomygigolo." But remember that this guy was called "Black Reaper" before he became a Contractor. Somewhat justified in that prior to Hei's He's Back moment solidified in this episode, Genma had pummeled him fairly easily in an earlier fight, although the ability of Hei to survive a beating from a psycho with Instant Armor power is itself impressive.
It's not the only time, either. Witness the woefully-overconfident assassin teams sent to kill him during the interquels; you'd think that nickname would be a bit of a tip-off, but this is apparently not the case.
In Mahou Sensei Negima!, upon arriving in a Magic world bar Negi is attacked by a random thug because he resembles a guy who beat him sorry many years ago - actually Negi's infamous father "The Thousand Master". In retrospect that should got him thinking...
Interestingly enough, Nodoka pulls this on the one of Fate's associates.
"You made the mistake of thinking of me as a mere powerless girl, Mr. Mage."
Anyone who ever thought that fighting Jack "Thousand Blades" Rakan is a good idea. Like Fate's minions believing they could take him on a 4 on 1 fight. He's the personification of awesome for a reason, people.
Durarara!!'s Shizuo Heiwajima, Ikebukuro's resident God of Destruction, doesn't particularly look like the sort of person who would (or even could) uproot vending machines and beat people half to death with them when he's not actively doing so. Thus, many people don't realize that it's a bad idea to pick a fight with the skinny guy in a bartender suit until it's far too late.
Many groups in Ichiban Ushiro No Daimaou seem to have Akuto in the sights of their manipulations, and casually talk about pushing him aside or disposing of him or some such, which would be incredibly stupid considering his "Demon Lord" status. And this isn't even getting into those dumb thugs that tried to pick a fight with him and instead ended up with broken limbs.
The title character of SWOT, Manabizaki, is a bespectacled nerd who studies too much. He has a Hair-Trigger Temper and a tendency to mouth off to people. Naturally, every delinquent in school was practically lining up to beat the crap out of him and put him in his place. After all, he's just an overly-studious nerd, ain't he? They'realwaysweaklings,right?
North Italy/Feliciano in Axis Powers Hetalia. This could arguably apply as well to Austria and Finland, given their histories.
The Thompson sisters in Soul Eater make this mistake regarding the skinny boy in the suit who comes looking for them. It's also noted in canon by Maka that Kid looks so 'low-key' and unimpressive that it's easy to forget he's a death god and so a very formidable opponent when he feels like it. His eccentric behavior only enhances that impression. A similar claim could be made about his father Shinigami, although all who have encountered him so far know what they're dealing with and are appropriately wary.
Not to mention Blair. Disregarding the fact that the series began with the protagonists overestimating her badassery, in the Clown arc she takes up about a third of the action fighting the Flying Dutchman, who thinks she's just an annoying cat. She kills him by stealing his hat and tricking him into committing suicide to get it back.
Characters underestimating Naruto more often comes because they simply knew him as a struggling ninja academy student, post time skip, it became less common, especially since he started win enough fights that would more liken make other afraid to take him on.
Kabuto is a repeat offender, even when, by all rights, experience should have taught him better. Then again, he is Smug Super and a colossal Jerkass. Surprisingly averted by Madara (the real one), of all people. He actually respects Naruto's abilities, and this is a guy who considers everyone but the First Hokage an unworthy challenge.
A lot of antagonists from Pumpkin Scissors think War Relief Section III is a group of incompetent idealists. They are quickly proven wrong when War Relief Section III manages to derail villains' plan all by themselves. Especially applies to Randel, a Super Soldier who can stop tanks on foot.
Monster: Several characters made the mistake of underestimating a certain blonde haired gentleman by the name of Johan Liebert.
Misaka Mikoto from To Aru Majutsu no Index is the third strongest esper in academy city, and everyone knows about her, yet for some reason delinquents frequently try to hit on her, generally resulting in them getting electrocuted. In fact, in the first scene of the first episode of the anime the main character is running from delinquents that he got to chase him because they approached her carelessly. in the end, she still zapped them.
There are only seven Level 5 espers in Academy City. Each is explicitly a One-Man Army and the stronger ones like Accelerator, Dark Matter, Railgun and Meltdowner are an outright Person of Mass Destruction. Fridge Logic would dictate that punks would get their photographs and avoid any of them at all costs but no, if you thought trying to punch out Mikoto was bad, there are idiots who try to attack Accelerator!
It only gets worse from there too. Later in the series, God (yes that one) is somewhere around thefifth strongest entity in the series, and the ones stronger than he/she/it are underestimated a fair amount. Like that one time Accelerator (not on that exclusive stronger than God list) tried to attack Aiwass (the strongest entity in the series). Aiwass' passive defenses would have killed him in his Super Mode. To put a comparison on their powers, Accelerator is to Aiwass as your average Level 1 is to Accelerator.
This tends to happen to Nanashi in Sword of the Stranger, since most of his enemies don't expect some random guy, armed only with a sword that he can't unsheath, to be able to kill several simultaneously attacking samurai. Which he does. Multiple times.
Firo Prochainezo from Baccano! is one of the Martillo family's top fighters, second only to Ronnie (who's more or less an Eldritch Abomination). He also a small, baby-faced pretty boy that looks so harmless that children think they can take him on without much trouble. Czeslaw finds this amusing.
A lot of vampires sent to defeat Alucard in the earlier chapters of Hellsing (mainly Luke Valentine and Allambra) have the bad habit, while perfectly aware of his reputation, of thinking of him as a simple very powerful vampire and believing they can take care of him easily. This usually lead them to a gruesome and horrible death when finding out Alucard is actually a Humanoid Abomination at his weakest, and will turn into an Eldritch Abomination if he happens to take the fight seriously.
Similarly, Zorin, despite being warned by the Major that Integra and Seras Victoria weren't to be underestimated, disobey orders and attacked the Hellsing mansion, assuming it was helpless without Alucard around. She ends up killing and insulting Seras Love Interest, leading her to evolve into an actual vampire and granting her a death that would have made Alucard proud.
The Supreme Kai in Dragon Ball Z both underestimates and overestimates badassery. He overestimates his enemies, even in cases where it's quite illogical, and is repeatedly surprised by how freakishly strong the Z fighters are. Had he come to Earth with a rational assessment of their power, rather than a poor assumption, things would have gone a lot better.
In Sangatsu No Lion, this is one character's fatal mistake during a shogi tournament semi-final match that results in that character's loss. He initially writes him off as just another opponent (reducing him down to just his rank) in his fervor to go up against another character in the finals, not realizing the accomplishments under his semi-final opponent's belt would indicate the true strength in his abilities.
An interesting case of this pops up during Bleach With the good guys(The Vizards, and various Soul Reapers) focused so hard on avoiding Aizen's Zanpaktou, which allows him to completely hypnotize anyone who sees its Shikai form, they forget one vital thing: Aizen is the strongest Soul Reaper next to Yamamato, and proceeds to demonstrate he doesn't need his swords powers to utterly crush them in battle.
In Black Lagoon, at the beginning of the first "Killer Meido" arc, some local yahoos make the mistake of thinking that Roberta is an easy target because she's a milk-drinking Meido.Bad mistake.
Later on, at the beginning of El Baile De La Muerte, some of them make the same stupid mistake about Roberta's protege Fabiola.You'd think they'd learn...
Anytime an outsider comes to Roanapur, they're either the biggest badasses around or complete morons. A perfect example would be when a Florida mafia enforcer tries to boss around the mercenaries he hired to capture Jane. Shenua calmly explains to him that they're not a bunch of "gangbangers who get off on graffiti-ing walls"; every one of them is a professional killer.
This happens a few times in Watchmen, especially a number of times with Rorschach: attacked by bullies when he was a kid, when he and Nite Owl hunt for info in a bar, when he's attacked in prison...
This is why Apollo and Midnighter lose to Captain Atom in Captain Atom: Armageddon. The pair think Atom is just another super-powered mook, not realizing that Atom is more powerful than all the members of The Authority combined, including Jenny Quantum. The only reason they last as long as they did is that Cap refuses to go all out against people he barely knows, even ones who are currently trying very hard to kill him.
Speaking of Nightwing...Oh, look at that the "Kid Sidekicks" think they're going to form a hero team of their own. Ha! Go back to school kiddies. Oh...you just knocked a world-destroying demon into next week and fought the JLA to a standstill in your first outing?
In the fourth and final issue of the JLA-Avengers crossover, the supervillain Prometheus, who can pretty much download any fighting capabilities he wants, confronts Captain America and says, "I've just uploaded Batman's fighting skills. That'll be more than enough to defeat you." Cap replies, "Oh?" On the next page, Cap is seen hitting Prometheus hard enough to break his helmet.
Happens to Spider-Man quite frequently. He's a lithe guy who swings around a lot, wears silly pajamas, and makes stupid jokes. New villains tend to forget that he's held his own with the Avengers, the X-Men, and fought just about every villain in the Marvel Universe. (The rule of thumb is, when he stops cracking wise, start running and you don't stop till you're out of New York state.)
Has happened a few times to Tony Stark, whether because his identity was still secret and therefore it's assumed that he's just a rich playboy who needs a bodyguard to protect him, or because it's assumed that he's helpless without his armor. The thing is, it's generally a bad idea to attack someone who's been taking lessons from Captain America for about a decade unless you're a professional, considering Tony once beat the crap out of a bunch of Skrulls who were pretending to be The Avengers, and he did so with his bare hands while naked and while his heart was slowly giving out. And then there is, of course, this immortal exchange:
King Mob: [after taking the unlucky localfirmly in hand] I'm telling you you're in the wrong film, Fatboy. You're not in the cowboy film you thought you were in. This is a different kind of movie. And you're in the scene where the redneck shitkicker picks on the stranger in town, only it's Big Arnie or a gang of vampires. I'll bet you've seen that a million times, Cowboy.
In The Hard Goodbye arc of Sin City, the bouncer for Katie's Bar throws out a customer, looks at Marv and tells him to leave. Marv calmly grabs his face, breaks his nose and goes in. The rest of the staff apologizes for the bouncer.
That entire story is set up by the fact that the all-powerful Roarks thought it would be a piece of cake to frame a murder on a big, ugly drunk, unaware that he was extremely dangerous.
Most people of Alysia in the first books of Les Légendaires mainly remember the Legendaries as a bunch of failed heroes who caused the infamous Jovenia Incident that turned everyone into a child when trying to save the world. As such, in the first books, their name wasn't even impressive to anyone, to the point two thugs are shown laughing when they introduce themselves. What those people tend to forget is that the Legendaries also foiled several times the plans of a much fearedSorcerous Overlord with a massive body count, and actually succeeded in defeating said Sorcerous Overlord. They fortunately get their respect back after the Anathos Cycle.
One especially hilarious example is during the fight between Razzia and Dark-Razzia, when Razzia announce he is going to kick his ass in memory of his sister:
In the Firefly fanfic Forward, this happens multiple times. The badguys repeatedly underestimate the crew in general and River and Jayne in particular, assuming the former is just a small teenage girl and the latter is just dumb muscle. In the "Last Man" story, the Six Rifles especially underestimate just how resourceful a young Jayne Cobb is when they take a contract to kill the robbery crew he was on.
In the Wrath arc, the Academy agents who defeated, captured, and interrogated River eventually conclude that she is a psychological wreck who underestimated their capabilities simply because she's a very dangerous psychic assassin. Then River reveals that she planned the whole thing and then cuts the power to the building while still tied to a chair.
The four, who mostly look normal and wimpy, take advantage of being underestimated whenever possible in With Strings Attached. In fact, they win the day because the skahs (and Jeft, for that matter) cannot conceive of them being competent, especially after George and Ringo are depowered.
In Things We Don’t Tell Humans, Jolt does this to Bumblebee. In the flashbacks, most of Terratron’s other students do this to Prowl when they first meet, and Megatron does this to Optimus Prime when they have their first "argument" as rulers. Starscream severely underestimates Faust, too.
Ultimate Sleepwalker: The New Dreams features Psycho for Hire Bullseye, who brags about being an A-list supervillain and mocks the supposedly C-list 8-Ball when they end up fighting during a Mob War. The ensuing fight ends with 8-Ball using his jet-propelled cue stick to flick Bullseye's detached head into a garbage can.
After Luso in The Tainted Grimoire failed the mission he gave him, several months later, Baron Popple doesn't think he could win against Suzuka. He was wrong.
Friendship Is Magic: The Adventures Of Spike: According to Spitfire, ponies tend to do this about the Wonderbolts, often forgetting that despite being most well known for stunt shows, they are part of the military. And they show it during the changeling invasion.
In the Harry PotterAUEmpire the Sorting Hat puts Harry in Hufflepuff so that he can have the advantage of everyone underestimating him.
A common theme with the newly human Biju in Eroninja is to underestimate everyone else. This includes Nel/Sanbi who was turned into a child, Urd who was born from a fragment of the Hachibi, and human opponents as well. They quickly learn that despite their appearance and origin respectively, Nel and Urd are Biju and that some humans can hold their own against a Biju, even if they can't win.
The cantina scene in the first Star Wars. A couple of criminals don't take too kindly to Luke Skywalker, and probably don't think the old guy with him would be much help in a fight. A few seconds later someone's lost an arm.
Jabba the Hutt came to power during the Republic's heyday. He survived the Clone Wars. He was positively thriving with the Empire. The Rebellion and Luke Skywalker probably seemed small potatoes compared to them. He was wrong.
In The Rundown, The Rock plays a "retrieval expert", and in the opening scene a client has sent him to collect a debt from a professional football player. Having approached the player in a club, he gets a drink thrown in his face before looking round to see that half the team has surrounded him. Sighing, he explains that they can do this the easy way or the hard way — they choose the hard way. Cue one guy beating up seven or eight huge athletes with ease.
In Shaolin Soccer, Mighty Steel Leg is beaten up in a bar because he's not allowed to fight back. The same thugs meet him on the street and throw insults. One of them throws a football at him, he kicks it back HARD.
Terminator 2: Judgment Day. The T-800 walks into a bar in the buff, tells some punk to give him his clothes and his motorcycle. The punk starts a fight. Guess what happens?
The biker punks of the original Terminator learned the hard way that they were Too Dumb to Live when he wanted clothes. They're lucky that the Terminator in question just let them live.
The Zatoichi series in Japan lives on the basis that people are always underestimating Zatoichi because he is blind, but is really an extremely deadly swordsman.
The head kidnapper (Richard Boone) can tell that the man following them is a Badass, and says as much; what he doesn't know is just how much of a badass he is, or how personally invested he is in the outcome of the situation.
Secondhand Lions: When Hub is harassed by a group of ne'er-do-well greasers in a tavern, he not only kicks their asses (FOUR to ONE) but takes them home with him and teaches them what it means to be a man. Bad. Ass.
In Ip Man 2, the friends of Wong Leung who he calls to challenge Ip think he looks like a laundryman, while one of the Hong Kong masters thinks his name sounds lame. They have no idea.
The opening scene of The Matrix has this with the cops ignoring the Agents' orders and trying to apprehend Trinity themselves.
Captain America in Captain America: The First Avenger, shortly after becoming a super soldier, thanks in part to Dr. Erskine's death, he was pretty much placed onto a USO entertainment group seeing how they don't really have much of a use for the supersoldier program. When entertaining American troops in Italy, the soldiers were not impressed with his performance (one of the soldiers was also implied to have mooned him, and they eventually pelt tomatoes at him while demanding for the girls to return). Of course, after he singlehandedly rescued 400 soldiers in one of Schmidt's bases, they began to realize he really is that badass.
Happens surprisingly often within Airwolf. Of course, most people don't count on a helicopter being more well-armored than a tank, being capable of flying at speeds up to Mach 2.5, flying into the stratosphere, and carrying enough firepower to wipe a small country off the face of the earth.
According to Tang Von Soong (referring to String, who is perhaps the world's best combat pilot), "Fortunately such people have little stomach for the nature of war".
Also happened with Robert Winchester, who was able to give String a run for his money in the Airwolf Simulator. The Firm restricted his role from potential Airwolf pilot to scientist because he didn't quite have the same "natural talent" for flying that String had.
When the title character of Hancock is serving time in prison, he is accosted by some thugs he'd gotten thrown in there. They attempt to threaten him, apparently forgetting that Hancock is a superhero on par with Superman, but with none of his sense of fair play or justice.
Taylor: 500 fights, that's the number I figured when I was a kid. 500 street fights and you could consider yourself a legitimate tough guy. You need them for experience. To develop leather skin. So I got started. Of course along the way you stop thinking about being tough and all that. It stops being the point. You get past the silliness of it all. But then, after, you realize that's what you are.
In The Avengers, Loki starts ranting at the Hulk as a mindless brute and his inferior. While this is an incredibly stupid act on anyone's part, Loki is quite arrogant, egotistical, and most importantly, a god. The idea that the Hulk could take him probably never entered into his mind.
For those who have not seen the movie, the Hulk proceeds to beat the "puny god" down like a freaking rag doll.
Almost a running gag in Christopher Nolan's The Dark Knight Saga, even among people who theoretically know what they're dealing with:
The Dark Knight Rises: Batman, who has been out of action for roughly eight years, gets back in the batsuit, and is able to hunt down and capture several League of Shadow members who were trying to escape a bank robbery. The primary villain Bane manages to get away. Batman dismisses Bane as just another one of Ra's al Ghul's flunkies. When Bruce and Alfred review tapes of Bane's assault on the bank, Bruce brushes away Alfred's assessment of Bane's combat abilities, stating that he'll simply "fight harder". He teams up with Catwoman to go underground and take out Bane, only to be outsmarted by Bane and lured into a trap. It's only thanks to the ensuing Curb-Stomp Battle that Batman realizes just how dangerous Bane really is.
In Star Trek: Into Darkness, when being questioned by Kirk, John Harrison makes a snide comment about Spock being a Vulcan and how Spock wouldn't know savagery like him. Spock proves him wrong when he delivers a brutal beatdown on Harrison/Khan after Kirk's death. There is a good reason why Vulcans suppress their emotions.
Elle in Legally Blonde is constantly underestimated and looked down on, simply because most people see her as a Dumb Blond. She proves them all wrong when she got into Harvard with a 179 (one mark away from the perfect test) score on the LSAT and again, when she used her knowledge of haircare, to win her first case. And she was only a first year law student!
This happens a couple of times in The Queen's Thief series. In The King of Attolia, Eugenides spends the whole book practicing only basic sword routines in the public practice courts, and then reveals himself to be the best swordsman any of the soldiers have ever seen by trouncing an entire squad. People always forget that he had two grandfathers.
This often happens to Eugenides, most notably when he manages to single-handedly destroy the house of Erondites, which was powerful enough to pose significant threat to the the Queen's reign, and, in the same scene, scares the crap out of his attendants and thus gains their loyalty.
Attolia: Ninety-eight days. You said it would take six months.
Euginides: I like to give myself a margin when I can.
He even lampshades it: "Has it occurred to you, Costis, that the only reason I'm alive is that those three assassins took me for a prancing lightweight?"
It's not a real fight, but in Wraith Squadron, the Wraiths ask Wes who the greatest pilot alive is, and Wes considers for a bit, then says it's their commanding officer, Wedge Antilles, because of his killcount and time in active service. Falynn Sandskimmer scoffs at this, says that he might have been good in the past but got old and became washed up. Wedge tolerates this for a bit, then challenges her to a race in ore haulers and wins handily after toying with her a bit.
How does he win? Amongst other things, he drops his ore hauler on top of hers, pushes off hers, and plops down right at the finish line. The only thing she can say? "You cheated." His response is yes, of course, because combat isn't a game. And if she wants to live through the war, she had best learn to cheat better. Of course, teaching Wraith Squadron to cheat might have been an example of Gone Horribly Right…
Also not a direct fight, but in several of Wedge's appearances in the New Jedi Order and later Legacy of the Force, people underestimate his abilities in all kinds of things. Not piloting, but things like the ability to tell when he's being used as a political pawn about to be sacrificed, and in general his extraordinary resourcefulness and endless skill with the Indy Ploy and, sometimes, Xanatos Speed Chess.
Most people don't take the three main characters too seriously, either, until they start winning. Meanwhile, Neville, Luna and Ginny ran a successful resistance against Voldemort's followers' rule of Hogwarts for the better part of the school year although it was made easier by Snape being a good guy.
Especially in the earlier books, where Harry, Ron, and Hermione are usually dismissed by older wizards because of their young age. Even in some of the later books, information is intentionally kept from them because other characters are worried it'll be too much for them to handle (which is sometimes true).
It seems that everyone (including himself) thought that Peter Pettigrew was a weakling. He was able to accomplish many feats of difficult magic, and was eventually responsible for the death of two of his old friends.
In Larry Niven's Known Space setting, the Kzin first encountered humanity in the form of an unarmed colony ship from a pacifist world, carrying only a skeleton crew. Seeing easy prey, they attacked. Unfortunately, "unarmed" and "pacifist" don't add up to "harmless"...
Discworld: "Sure, she's wearing the uniform of the City Watch, but she's just some pretty blond. How tough can she really be? Let's take her hostage again!" Protip, criminals: Captain Angua von Uberwald is also a werewolf, and one of the toughest and most dangerous members of the City Watch.
Carrot(As Angua is taken into a bar): Try not to hurt anyone.
Thug: As long as you do what we say, she'll be fine.
Carrot: Sorry, was I talking to you?
Also from the Watch, almost every antagonist will eventually underestimate Vimes and/or Carrot's ability to foil any Evil Scheme, regardless of the odds involved.
Cohen the Barbarian often gets this. He is a very, very old barbarian hero, but people tend to forget that in this line of work, one doesn't live that long unless they are very, very good at it.
Lu Tze of Discworld fame does his bit to spread rule number one: "Do not act incautiously when confronting little bald wrinkly smiling men." Most of the population is more than willing to go along with this rule. When he meets those few who don't, he has to educate them in why the rule is in place.
This seems to happen to Granny Weatherwax in about half the books she's in. The other witches get it too, but it's generally Granny who puts them down.
In The Dresden Files there are a good dozen or more of persons or entities who look weak, pathetic, foolish, dim, and easy prey. They are not to be laughed at. They are not to be looked down upon. They can and will kick your ass, if they don't just kill you. Here is just a small sample of the most frequently occurring examples.
So there's this guy. He's a tall but gangly fellow, looks perpetually unshaven, wears a big coat and walks around with a big stick and generally seems like a scruffy, weird sort, but is otherwise not really all that much of a threat. A great many people, both Muggle and supernatural, consider him to just be some freaky guy with eclectic fashion sense. Except this guy's name is Harry Blackstone Copperfield Dresden, titular character of The Dresden Files. Conjure by it at your own risk. After all, this is the man who has taken on all kinds of supernatural beings and survived every encounter. He killed a Faerie Queen, stared down and nearly killed Nicodemus Archleone- twice, reanimated a dinosaur and marched it through the streets of Chicago, and genocided the entire Red Court of vampires because they took his daughter. The supernatural types eventually start coming to realize how dangerous he is, but the muggles? Not so much.
So, there's this short woman, 5 foot tall, and like the example below, about 100 pounds. Head of the Special Investigations department for at least 8 years, while most last 2 weeks. Shot a half-ton werewolf monster from point-blank range. Once killed a plant monster with a chainsaw, and hamstrung an ogre with the same. One-hit-killed a Physical God with a holy sword, after having cut through countless Elite Mooks, any one of whom could tear an ordinary human to pieces. She drove away a Fallen Angel by drawing the same sword about 2 inches out of its sheath. Later, she killed a Faerie Queen that was about to kill the man she loves. And that is only the beginning of how extremely Bad Ass she is.
Ebenezer McCoy: An old Scottish redneck living on a farm in the Ozarks. Sounds relatively harmless? He's one of the most powerful wizards in the White Council, and fuck with him or his loved ones and he will pull a satellite out of orbit and drop it on your head like squashing a bug. If that is not a viable option, he will simply kill you with a wave of his staff. With one wave, he killed about 100 Muggle mercenaries.
Ivy, the Archive: A tiny slip of a girl who is the repository of all human knowledge, and can blast a fallen angel into oblivion with an Offhand Backhand. Remember, knowledge is power. She has a LOT of knowledge. Ergo, she has a LOT of power. Q.E.D.
So, there is this small fairy named Toot-toot. He is about 12 inches tall. He cannot understand complex orders as he has a very Literal-Minded. And he is a pizza addict. But he is incredibly quick, able to change directions on a dime, and with his trusty box cutter, he will take on a Skinwalker. Slicing into the ancient evil. Even one of the most powerful wizards in the world was impressed by how well he handled himself against a Physical God-tier force.
So, there's this guy dressed in what seems to be a pretty authentic recreation of a full set of Centurion armor. He has a cigar and is just generally wandering around being smug and arrogant. Then he uses half of Harry's Name to bring him to his knees with no particular effort when Harry starts giving him lip. This guy just so happens to be Ferrovax, the single oldest Dragon alive and is by Word of Jim a being that could go toe-to-toe with Mab, the Queen of Air and Darkness.
Donar Vadderung is not the head of the organization that hires out people like Gard as hired guns for no reason. When Harry seems to be taking his power lightly (specifically, the power of a dozen beings he describes as being not quite as strong as he is), he gives a little demonstration via slamming Harry into the ground with his raw will, leaving Harry as helpless as an "insect watching the shoe coming down". Even weakened, the guy is still a Person of Mass Destruction. This makes sense, considering that Mr. Vadderung is actually, literally, a Physical God. Odin to be precise. And if you're to young to comprehend how scary that is, he's also Santa Claus. Be afraid.
Vin from the Mistborn series is another one of those five-nothing, hundred-pound girls who's constantly overlooked and underestimated because of how unimposing she looks. She killed a Physical God, vertically bisected a man and his horse, headbutted someone in the face hard enough to reduce his head to Pink Mist, and has abused her Super Strength so much that she's essentially dependent on it to function, but also gets about three times more power out of it than anyone else. Most amusing when she's facing Koloss; they tend to get very confused while she slaughters them by the hundreds because they don't get how it's even possible for someone so little to beat someone much bigger.
Sienkiewicz Trilogy has a glorious example at the beginning of the second book. The protagonist, Andrzej Kmicic, mocks his opponent, Michał Wołodyjowski, before their duel. What happens next is such a one sided fight that Kmicic ends up begging his opponent to just kill him already and spare him more humiliation.
As you might expect in a military SF series, Honor Harrington contains a goodly number of examples:
Right off the bat, the enemies of the titular heroine regularly find, to their regret, that she's not as easy a target as they first thought:
In the backstory a fellow midshipman at the academy tried to rape her in the shower, not realizing she was a heavyworlder in Earthlike gravity. She beat the shit out of him, but unfortunately wasn't brave enough to press charges.
In Field of Dishonor, a professional duelist hired to kill Honor dismisses her as a serious threat on the dueling field, though he grants that she is a capable starship captain.
In the next book, Flag in Exile, she gutted and decapitated a trained swordsmen in one movement after having only spent a few months learning the sword, in part because her opponent was in the mindset of winning swordsmanship tournaments, not killing opponents.
One of the major villains in Honor Among Enemies dismisses Honor as a threat when taking her as a hostage... right before she cold-bloodedly guns down some pirates with an antique weapon, and reveals that she has arranged for the pirate shuttle that was trying to escape to be rigged with a bomb, destroying them before they could get away.
A less conventional example comes in the form of Manticoran Admiral Augustus Khumalo: his own navy considered him to be a by-the-book political appointee lacking both imagination and tactical and strategic experience, but when Terekhov discovered Mesa's plan to conquer the Talbott Quadrant, he demonstrated a tough-mindedness and adaptability that none of his fellow officers anticipated by backing his subordinate to the hilt, even at risk of war with the Solarian League.
On the level of fleets, rather than individuals, the outcomes of not a few battles are radically affected by one side learning that the other's hardware is a lot better than anticipated — starting in the very first book, when the Manticoran light cruiser Fearless goes toe-to-toe with a massive Havenite Q-ship. The Lensman Arms Race that follows results in a lot more such surprises from both sides, especially when the Solarian League — whose peacetime navy was, as of the first book, roughly on par with Manticore — discovers what happens when you join the arms race late.
Ranger's Apprentice: Halt is rather short, wears a mottled cloak, rides a shaggy pony, and has unevenly cut, greying hair. Underestimate him at your own risk.
In the backstory of Empire of the Ants, the whole ant population of France severely underestimated the Dwarf Ants, believing them to merely be small, weaker ants. In the following days, they took over Black Ants, Red Ants, Wasps, Termites... When the protagonists Red Wood Ants finally confront them, they discovered to their horror the Dwarf Ants had several queens in each of their colony, making them dangerous Zerg Rush specialists, and possessed high intelligence for the specie. By the time the story has started, the two species has become nemesis to each other.
In the Sherlock Holmes short story "The Speckled Band", Dr. Roylett, having learned that his step-daughter paid Holmes a visit concerning the suspicious nature of her sister's death and the strange atmosphere now surrounding her, attempts to intimidate Holmes by bending an iron poker with his bare hands. After Roylett's departure, Holmes, now even more interested in the case than he already was, informs Dr. Watson that had Roylett stayed, he would have seen that Holmes possessed an even level of strength by bending the poker back to it's proper form.
In the Robert Browning telling of "The Pied Piper of Hamelin", the Mayor and Corporation (his advisors) decide to renege on their promise to pay the Piper the agreed-upon fee for ridding the town of rats. Their thinking is that since the rats were drowned and "What's dead can't come back to life", there's nothing the Piper (a wanderer whom they regard as beneath them) can do in retaliation for the promise being broken. He warns them that he can use his music as an instrument (so to speak) of revenge, but they don't take the threat seriously and effectively dare him to try it. They learn to their eternal sorrow that his music also works on humans — specifically, children.
In The Tome of Bill, Sally is frequently subject to this. Marlene and Jeff/Night Razor knew her before she became a vampire and was just a normal human. They learn the hard way that Sally's probably the biggest badass in the series.
Taking time out of your life expectancy to gloat at or belittle AryaStark gives her more time to make you feel very, very sorry you bothered, for instance.
Or, how about laughing in the white-haired old man's face or just dismissing him as "old"? If that's SerBarristanSelmy, you've just proved what a jackass you are.
And, heaven help you if you insult Tyrion's intelligence by assuming he can't talk himself out of the bind you've just put him in: the odds are good that he can.
But, to win a Crowning Moment of Underestimation... you have to beat Kraznys mo Nakloz, a Good Master of Astrapor for his underestimation of Daenerys Targaryen. Repeatedly insulting somebody you should very well know for a fact is descended from an exiled branch of Valyarian Dragon Lords in the Valaryian language over several days is... a bit crass, but kind of understandable. They were the historical masters of your city and you hate them, so getting your digs into one of their few remaining descendants makes sense. Convincing yourself, however, that this mere slip of a girl without much visible backup won't be able to understand you or the nature of the very dragon you hope to gain in trade is... dumb. Handing her the army of invincible, obedient slaves in the middle of your (now) poorly defended city before full receipt (and control or containment) of the mobile flame-thrower you then precede to yank the chain of (literally)? And, um... you were calling her stupidly new to this whole negotiation thing, Mr Charcoal Briquette?
Live Action TV
Angel played with this trope in the first episode. Cordelia suddenly realised her potential sponsor was actually a vampire and Angel appears on the scene. When her fake sponsor doesn't seem at all bothered by Angel's appearance, Cordelia realises that it's because he not only doesn't know Angel's a vampire, but doesn't know just how dangerous a vampire Angel is. Unfortunately, her gloat of "You don't know who he is, do you? Oh, boy, you're about to get your ass kicked!" backfires. Not only did the vampire not know who Angel was, but Angel and Cordelia didn't know who he was. Turns out, the ones doing the underestimating were actually Angel and Cordelia. By the end of the episode, this situation has been very much reversed. Permanently, one might say.
And in the season 5 finale of Buffy, right after a Previously On summing up the entire series to date:
VAMPIRE: *moving towards Buffy* I don't mind a little appetizer...
BUFFY: You ever heard the expression, "biting off more than you can chew"? Okay... um, how about the expression, "Vampire Slayer"?
BUFFY: Wow! Never heard that one? Okay, how about, "Oh God, my leg, my leg?" *breaks his leg*
VAMPIRE: Oh God, my leg! Ah!
The basic premise of the franchise is to make the 90-pound cheerleader that the monster corners in an alley capable of ripping its arm off.
A non-monster instance occurs when Buffy squares off against Tara's father in "Family". Mr. Maclay has no idea that Buffy could kill him with her bare hands and, given what a mysogynistic Abusive Parent he is, it's a real shame we don't get to see her show him.
Multiple times on Burn Notice, especially in "Rough Seas", when Michael poses as a nervous nerd with an inhaler... only to turn on the group of drug dealers he's infiltrated when they least expect it. Also notable is "Bad Breaks", in which a bank robber has the bad luck to rob a bank with both Michael and Agent Jason Bly inside.
He's had it done on him once or twice; Lucy Lawless as an assassin pretending to be a "battered housewife" who needs Mike to find her husband comes to mind, as does Harlan and the nerdy "auditor" who is a good enough killer to pose a challenge to Mike in hand-to-hand.
Michael lampshades that the Coast Guard is generally seen as not very powerful. He then explains why this is not truly so.
Most people don't think the Coast Guard as being particularly well-armed. Most people are wrong. A Coast Guard patrol boat carries three .50-caliber M2 Browning machine guns and a 25-millimeter cannon, which means it can take out anything short of a battleship.
Babylon 5 episode "Ceremonies of Light and Dark". Marcus the Ranger is looking for information on some crooks who have kidnapped his friend Delenn. He joins a poker game at a tough bar in down-below and asks his contacts in the criminal underworld if they have any information to share. They decline, and ask why they should help him with this.
When we come back from commercial, Marcus is holding the beaten and bloodied last person from the entire room of thugs who isn't quite unconscious yet, who is quickly blubbering out that he doesn't know anything anyways, before collapsing into unconsciousness. An exasperated Marcus complains to no-one in particular, "Bugger!Now I have to wait for someone to wake up!" He then is surprised when someone else comes into the bar: Lennier, the mousy, quiet, inoffensive diplomatic aide to the kidnapped Delenn. When Marcus grabs Lennier during their discussion, Lennier picks him up by the neck and calmly reminds Marcus not to underestimate him. Marcus, who has just kicked the crap out of several dozen criminal thugs and assorted underworld hard-cases, thus proving his badassitude beyond doubt, is forced to back down—to another character whose badassitude is perhaps even more underestimated. (Of course, a few moments later another thug finally wakes up, and out of fear, gives Marcus the information he wanted.)
As might be expected from the above example, Lennier is also prone to this. During the first season, his fighting skill is a surprise to the audience, but once it's established, he continues to use it to surprise other characters.
On one episode of Magnum, P.I., a Chinese assassin is asking a big hairy sailor where the MacGuffin is hidden. The Chinese assassin is an insignificant looking fellow with glasses. But when the bargaining becomes heated, the assassin kills the sailor with his bare hands in half a second and isn't even breathing hard.
In another episode, Higgins goes off to an island on a camping trip with some boys from juvenile in a rehab program. They mutiny, but find out that Higgins is a Retired Badass.
Chuck does this a lot to enemy agents who don't know what he is - his fight scene in "Chuck Versus the Beard" is a prime example.
Caine on Kung Fu is always underestimated by people who end up getting their ass kicked by him.
Happens occasionally to Dr. Daniel Jackson of Stargate SG-1. In one particular instance, someone called him a geek while he was under the influence of a physically enhancing alien device. This device also increased aggression and impulsiveness (Dr. Jackson is not usually a hothead). It... didn't end well for said someone.
Also happened to Carter on occasion, due to her being an attractive woman. In particular, in the episode "The Warrior", a group of free Jaffa are disappointed by the Earth-based weapons they have been provided so O'Neill has Carter demonstrate how effective the weapons are. You can see the patronizing expressions as the Jaffa doubt both the weapons and the female's shooting abilities. Needless to say, Carter proved them wrong on both accounts.
O'Neill: This [Jaffa staff weapon] is a weapon of terror; it's made to intimidate the enemy. This [Earth P90] is a weapon of war; it's made to kill your enemy.
Ba'al, as a Politically Incorrect Villain, insults Carter's intelligence REPEATEDLY, even after she's saved the world a few times. After she slugged him in the face, though, he seems to have wised up.
How often do the bad guys of 24 think they've got enough security to protect themselves from Jack Bauer?
Also, if you get any ideas about going after Abby... She can kill you and not leave any forensic evidence.
Doctor Who. "Oh look, here comes this weirdo in stupid clothing. He couldn't possibly be that smart...how dangerous could he be?" Just... look him up.
the double episode Human Nature / The Family of Blood involves a family of short-lived aliens named the Blood Family chasing him in order to consume him and gain immortality. The Doctor initially tries to escape from them by sealing his alien self while he turns human with his companion Martha as the one in charge of his former self. The Blood Family then goes after them, killing several people in the process and bombing a village to force the Doctor to come back. When it finally happen, an infuriated Doctor easily Out Gambits them and punishes them by putting them in various And I Must Scream situations that specifically grant them eternal life in the process. They then realize he wasn't running from them because he was afraid of them... but because he was afraid of what he could do to them.
" Subject Is Unarmed." "Ya think?" This was said to a Dalek Rory Pond, a nurse who is one of the most hardcore beings in the universe.
Nick Burkhardt from Grimm is subject to this a lot, like when a group of coyotls thinks he and Hank are just two cops with no idea what they are getting themselves into in addition to being out numbered, or in the rare instance where he gets to pull this on someone who knew he was a Grimm when the Reaper dispatcher sends two Reapers to catch him by surprise, only to get a rather disturbing package in the mail.
Farscape brings us John Crichton. A human from earth—a planet that hasn't even been to its own moon in almost 30 years at the time the series started—who in early episodes is constantly dealing with the scorn of the more "advanced" members of Moya's crew. And he saves their asses every. Single. Time. By the end of the first season he's finally earned their respect and friendship. And then it's time for him to do the same with his enemies:
Crais spent almost a cycle trying to capture him before Scorpius finally gets his hands on him purely by chance. Crais's failure to bring Moya in didn't exactly sit well and made him something of a laughing stock. And then Scorpius found out first hand just how dangerous and resourceful Crichton is.
Genre Savvy that he is, Scorpius was less likely to underestimate Crichton, but even then John still had his moments where he took him by surprise. Grayza, on the other hand, was completely incapable of recognizing the threat Crichton actually posed. Especially when the rest of the galaxy was pointing and laughing at the Peacekeepers' inability to recapture Moya.
This gets deconstructed in Kamen Rider Wizard. One of the villains is a quirky character by the name of Sora who manages to be an annoyance to the other villains, including the Big Bad Wiseman once he frees a rather destructive Phantom. Almost everyone underestimates Sora's true potential and just consider him write him off as "that annoying Phantom". Heck, even the main character, Haruto, began to underestimate him. At that point, we find out that, yes, there's more to Sora than meets the eye. He was a serial killer prior to being a Phantom and has his sights on the Philosopher's Stone, a MacGuffin that the Big Bad has in his possession. Once it's made clear he's after the stone, The Wiseman tries everything in his power to kick his ass, though leaves him just kicking, underestimating him. It becomes Wiseman's hubris as Gremlin, on his second attempt, snatches a weapon from him and kills him with it, then steals the role of Big Bad. Bottom line: Never underestimate the quirky Phantom, or else everyone is screwed.
This is something that the Big Bad had a case of twice. The only reason his plans were foiled in the first place was because he didn't account for Nitoh, a Big Eater, unleashing his Phantom, an even bigger eater to consume all the Mana he needed to execute his plan. You can say that underestimating badassery is a Fatal Flaw for him.
Person of Interest has thugs constantly underestimating Reese due to him wearing nice suits and working alone. Half of these encounters only show the thugs getting ready to attack and later Reese walking away from a pile of groaning men.
Season 3 of Justified is built around this trope. Detroit mobster Robert Quarles repeatedly underestimates just how smart local gangster Boyd Crowder is. Boyd, for his part, expects that Quarles being a Fish out of Water will be completely ineffective in Harlan County. He's right, but what he doesn't take into account is just how physically dangerous Quarles can become when cornered.
In Supernatural, no matter how many monsters, demons, or other enemies the Winchesters have killed, they're almost always underestimated by whatever enemy they're facing. One notable exception is Crowley.
Kenny Rogers' "Coward of the County" - a man who took an oath to never resort to violence, comes home and discovers that three men had gang-raped his wife. He tracks them down to the bar they were drinking at. One goes to confront him and he turns right around and, as they laugh, walks back to the front door. Then he locks it so they won't be able to run away from the aggression he's been bottling up for 20 years. When he's done, not one of them is still standing.
He then stands there and apologises to the soul of his dead father for not being strong enough to walk away from this one.
In Traveller one of the main reasons the Terran Confederation defeated the Vilani Imperium was that the Vilani, at first didn't think much of Terra and effectively thought of themselves as trying to "arrest" it rather then trying to "conquer" it. They found out that Terrans were warriors.
Happens absurdly often in Warhammer 40,000, to the point where one wonders how these individuals have managed to survive for so long considering they tend to die horribly after severely underestimating their opponent. Examples include but are definitely not limited to Imperial Guard thinking that Orks are mindless brutes, Orks thinking Imperial Guard are just skwishy humies, Space Marines thinking filthy Eldar are no match for their zeal, Eldar thinking Space Marines are foolish primitives, everyone else thinking Necrons are just machines, Necrons thinking everyone else is just defenseless food... it happens a lot, is what I'm saying.
The most ironic example is Ciaphas Cain, who honestly believes he's an abject coward. Except events and his own better nature keep conspiring to make him a hero. Despite his claims, he is genuinely brave on more than one occasion. At one point, he tries desperately to get back to an isolated friend who's about to be overrun, and blames it on some sort of head injury.
A common meta example in Vampire: The Masquerade - often, many fights are between the player characters and human gangbangers who don't know that the people in front of them can, among other things, punch through walls, take a shotgun blast to the face, outrun a high-speed train or swing a longsword with one hand. And how the players love it.
As a general example, NPCs have an alarming tendency to underestimate the player characters' ability to get the job done.
During the same mission Shepard can order a turian to stop harassing an asari. If Shepard is female, the turian will even make an advance on her. No matter the gender, it ends with said turian being thrown across the room.
Despite knowing that Wrex, the most powerfulkrogan on Tuchanka, has nothing but respect for Shepard, that Shepard has the balls (regardless of gender) to headbutt a krogan chieftain to get him to shut up (a species strong enough to snap a human's neck by backhanding them), and has personally witnessed Shepard and buddies not only survive but possibly kill a thresher maw on foot, something that has not been done in centuries (and the last time was by Wrex), said aforementioned chieftain still thinks he can take Shepard in a fight.
In the Arrival DLC, Shepard is captured and sedated by an indoctrinated scientist, who has him/her locked up with a small army of indoctrinated soldiers outside. This...doesn't work out.
Project Guard:Shepard is tearing us apart!
Shepard was the last person for who knows how long to kill a Reaper. The Reapers and the Collectors still believe him/her to be just one person... at least until the end of ME 2.
Garrus:Honestly? The Collectors killed you once and all it did is piss you off. I can't imagine they'll stop you this time.
And Harbinger has actually acknowledged that s/he is disrupting their plans. Coming from a member of a race of ultra powerfulCthulhu-esque starships, that is SERIOUS badass cred.
The Illusive Man, even after being indoctrinated by the Reapers,has a great deal of respect for Shepard. His underling Kai Leng, on the other hand, ignores his advice on how dangerous Shepard can be. It ends badly for Kai Leng.
Less destructively, Vega challenges you to spar when you get the Normandy in 3, on the logic that you're just as human as he is. After the opening to 2, as a result of which you're 30% cybernetics and able to wield shotguns and sniper rifles with enough recoil to break a normal human's arm...yeah, you're not quite as human as he is, and despite Vega's massive muscle development, it's almost certainly going to end with him getting flipped, quite possibly by the comparatively slim female Shepard.
In Dragon Age: Origins, there are only two Grey Wardens remaining. One is you, the other one is in your party. Everybody still thinks they got a chance against you. Lampshaded by a guard after witnessing you fight:
In the sequel, this tends to happen as well, despite the entire point of the start of the game being about increasing your reputation/infamy. You still get people thinking you're "all hype" even after you get to Act 2, wherein you've reclaimed your family's noble status and bought back your ancestral home through acts of sheer heroism - specifically delving into parts of the Deep Roads that makes everyone short of the Legion of the Dead soil their armor - and have everyone up to the Arishok respecting you... Or at least having a "growing lack of disgust" for you. The fact that anything short of an entire army is willing to stand up to you and your comrades by Act 3 is the height of foolishness.
In the Fable series, even after the history of superhuman exploits you have well into the game, common thugs and bandits will still voluntarily attack you. This is particularly Too Dumb to Live-ish in Fable 3, where people will attack you when you're King, despite knowing of your Badass lineage and the fact that you are the only thing capable of saving Albion from certain doom.
Assassin's Creed II: Likewise for Duccio de Luca picking a fight with Ezio Auditore da Firenze thirty years after Ezio publicly beat him for infidelity against Ezio's sister. The reason Duccio dares to do so? He's got a few unarmed thugs for muscle, while Ezio's alone. Veers into Too Dumb to Live though, that Ezio by now was the man who fought off the would-be killers of Lorenzo de' Medici, participated in the Forli succession conflict, killed Girolamo Savanarola, fought the Borgia family guards at the bridge to the Vatican district, and even openly took to the streets to drive Cesare Borgia from Rome… all of these incidents being in public, with witnesses, and Ezio wearing the Assassin Robes. On top of that, before this Ezio was (even after his exile from Florence) had been a recognized absentee lord of the castle-town of Monteriggioni, making him a semi-public figure.
Mega Man X suffers from this quite a few times. Being a centuries-old "robotic relic" who is also a Technical Pacifist, many reploids think he'd be a cinch to defeat despite the fact he's a famous Maverick Hunter. They're more than a little surprised when he destroys them.
The Day of Sigma OVA basically centers around Sigma vastly underestimating X.
Many Mega Man Zero bosses mock Zero's "Legendary Hero" status and the fact that he was out of commission for about 100 years since the X era. How wrong they are.
Touhou characters never seem to realize that fighting Reimu or Marisa is a bad idea. Considering the former can make herself completely invincible at will, the latter can obliterate continents, and both of them have fought and won against some of the most horrifically powerful beings in existence, it is no wonder the string of pathetically weak individuals that keep challenging them to fights don't exactly leave unscathed.
A rather interesting example in Vampire: The Masquerade – Bloodlines: for most of the game, all of your enemies underestimate the "newbie vampire". It's semi-subverted near the end when everyone seems to realize "holy cow, how is this days-old vampire surviving all of these suicide missions?!" By that point, half of the Elder vampires want you on their side. The other half, sadly, see you as a threat and fall back into this trope by trying to kill you.
Potentially a Justified Trope. The relative power of vampires is usually a combination of generation and the amount of time since being embraced. Typically, the player character would be expected to be thirteenth generation, at best, which used to be believed to be the weakest possible generation for a vampire for most of the setting's timeline. The blood points at character creation indicates the player is an eighth generation vampire (although this is never explicitly mentioned). It has been over 700 years since it was common for newly embraced vampires to be eighth generation, so it's hardly surprising there is a tendency to underestimate them.
In the Civilization games, the NPC leaders will often make disparaging comments such as "your army is the laughinstock of the world" if you happen to have a smaller military than they do. They tend to fail to take into account things like technological advances.
This also happens in Galactic Civilizations, despite the designers claiming that their AI is markedly superior to that of other 4X games. A computer player may have a bigger fleet than you and may even be slightly more advanced but will completely discount your industrial capacity. What this means is that you can build a fleet twice the size of his in the time it takes him to get his fleet to your planets (and computer planets are notorious for declaring war first and preparing for it after).
In The Elder Scrolls V: Skyrim, one would think that a memo would have been sent to all of the Nine Holds warning everyone not to threaten the Dragonborn, who routinely fights Dragons single-handedly. They generally learn their error within a few moments of hearing "FUS RO DAH!"
Taken to an extreme by the Thalmor, who despite having the military strength to threaten the Empire, only ever bother to send up to 3 mooks after you at a time, even though they potentially may have suffered dozens of casualties at your hands.
The Godfather 2: Every one of the enemy mob bosses you meet talks smack to you, with Michael himself joining in at times. Regrettably, there's no Enemy Chatter for you to get the satisfaction of hearing them take their words back as you kill them off.
The Exile in Knights of the Old Republic II: The Sith Lords gets this a lot for someone whose status as a Jedi Knight and ex-war general is common knowledge. Early on in the game, your party is being held under arrest on Telos and a bounty hunter breaks into your cell to try and take you in to collect on a bounty. Because it's not as if a Jedi Knight has the power of the Force or anything, ri—...oh wait...
In The Force Unleashed, General Rahm Kota seriously underestimated Starkiller in their first meeting.
Kota: A boy? Months of attacking Imperial targets, and Vader sends a boy to fight me?!
In the backstory of Star Trek Online, Ja'rod, son of Torg, a Klingon Defense Force officer and a minor nobleman, was on vacation when a trio of Undine infiltrators attempted to Kill and Replace him. He killed two of them and tortured the third into revealing its species' Evil Plan.
Xykon runs into this a lot. Most people who meet or see him for the first time assume that, as a 'walking villainy cliché', he must be very easy to get rid of. And while Xykon is in no hurry to prove them wrong, he's incredibly powerful and devious. Both Roy and Vaarsuvius thought they could take on the lich single-handedly, and nearly paid the price. Roy died in his second attempt, but got better. So far, the only real threat to his existence was the ghost-martyr of Soon Kim.
Jade Sinclair (Generator) of the Whateley Universe gets this a lot, because she's a petite, pretty teenager who looks like a ten year old Japanese girl. When she is attacked by Bloodwolf and Maggot and Killstench simultaneously, she knocks two out (breaking one's jaw) and takes out the unstoppable Bloodwolf (who can heal from any injury) by nailing him to a tree. With railroad spikes.
A Running Gag in the comments section is that pretty much everyone's reactions to Skitter is "Meh, I could take her." One person noted (Somewhat inaccurately), That there were only two exceptions to this in the entire story, namely Sundancer and Citrine. Amusingly, Citrine is one of the few capes at that point in the story that Skitter is nervous about fighting (If not outright afraid), thanks to her ability to turn people's powers against themselves.
Eventually, the PRT learns not to do this: they specifically say, "Look, take our rankings for her, and treat her as though she were two rankings higher across the board." They decide to treat her as though she were a Brute, a Breaker, and especially a Trump of some degree. It doesn't help much, but at least they tried...
Batman gets this too, just like in the comics - notably from Dr. Destiny in "Only a Dream":
Dr. Destiny: But you're different. You don't have any special powers.
Batman: Oh, I have one, Johnny: I never give up.
Also from the DCAU, elderly Bruce Wayne does this all the frickin' time on Batman Beyond. Proof? Go to the Batman Beyond CMOA page and find all of the Old Bruce Entries. 99.9% of those are this, the other .1% is ass-kicking resulting from this.
Jokerz Leader: Who do you think you're talking to, old man? We're the Jokerz.
Bruce Wayne: (dryly) Sure you are.
Payback: You're a mean old man, you know that?
Bruce: Mm-hmm. And what are you?
Payback: I'm your worst nightmare!
Bruce: You have no idea what my nightmares are like.
This is one of the primary themes behind the Superman: The Animated Series episode "World's Finest", which brought Batman and the Joker into the picture. Both Superman and Lex Luthor see both the Joker and Batman as non-superpowered beings not worth their time and energy. By the end, Batman has scared the crap out of Luthor (something even Superman never even managed) by breaking into his penthouse, and the Joker comes closer to killing Superman than just about any other villain had previously, almost kills Luthor, takes over the mob, and almost levels a good portion of Metropolis to the ground.
And Zhao does it again against Aang in a later episode; when warned by his former master that he is not ready to fight the Avatar, Zhao arrogantly replies "I think I can handle a child". The result? Aang makes him look like a fool by tricking him into destroying his own fleet, thus defeating him without landing a blow. Obviously, Zhao never learns.
On the surface, Zuko's Uncle Iroh looks like a quirky old man who'd rather do little else besides sleep and drink tea. Of course, he's exactly that, but he's also the Dragon of the West and will kick your ass six ways from Sunday if you give him a reason to. There's more than a few of his foes that don't seem to get that.
The sequel The Legend of Korra keeps in this direction: while Yakone wasn't exactly a poor villain (he was a dangerously skilled Bloodbender and a Crime Lord), he did underestimate Aang according to the flashbacks, mocking him and telling him he dealt with people like him before and would do it again. Apparently, he forgot Aang was the Avatar, meaning a guy connected to the Spirit World and controlling all elements. So it's not that much of a surprise when, during their confrontation, Aang just went avatar state, immobilized him and took away his bending.
Similarly, Yakone's son Tarrlok severely underestimated Amon when confronted by him and ended up with the same fate.
Also from Legend of Korra, Vaatu disregards Wan, saying that a mere human is no match for an immortal spirit like him. He's right, until Wan fuses with Vaatu's Arch-Enemy Raava and becomes the Avatar.
When Captain America escapes imprisonment inside the Skrulls' ship in The Avengers: Earth's Mightiest Heroes, the Skrull commander immediately assumes there is no need to bother because "This man isn't a threat. There is nothing special about him." A few minutes later, Cap has freed all prisoners onboard, convinced all of them (some of them being villains) to team up and led them to a ship which they use to escape. The Super-Skrull even lampshades his commander's stupidity and tries to kill Captain America, declaring him too dangerous to be left alive.
Ben 10: the title protagonist tends to get this a lot, especially in the original show, because he is 1) a human in a universe where his species is considered primitive and 2) a kid who happened to end up accidentally in charge of the most powerful weapon in the universe which he barely understands. However, he turns out to be quite good at using it, and only get better with time. Eventually, the villains who already clashed with him before are Genre Savvy enough to warn their minions about not underestimating him (Ghostfreak once beat up his Dragon Dr Vicktor for believing Ben was not worth killing). In the sequels, however, Ben's mutiple exploits ended up making him a Living Legend, and most villains are careful about not underestimating him.
One of the most noticable cases of this trope is Simian, an Arachnichimp Con Man who wrongly assumed he could easily fool Ben into doing his job for him by making up a sad story to attract his sympathy. Ben went along with it, but, by the end of the episode, we find out he actually had started to figure out the truth around half the episode, and alreadyOut-Gambitted Simian. The poor alien con man ends up finding out about that far too late, when he is already in presence of his very pissed off hirer...
Rook: Not so green that I let a tunnel collapse on me!
Kim Possible: Ron Stoppable is constantly considered a fool and harmless by villains...at least until he causes their lairs to blow up. The ones who really underestimated him and paid the price were the Alien Invaders that attacked the Earth in the Grand Finale, who planned to make Kim into a trophy. Big mistake.