Ranma ½. Everyone knows some martial art variation, from Anything Goes Tea Ceremony to Martial Arts Figure Skating. You name it, it's a martial art. Even calligraphy.
The Mons genre in general. Every opponent the main character meet will inevitably have a theme to their item or pet, which they will invariably ALSO be a martial arts master in this style as well. As they scream out the names of the attacks their item or pet does, they will also (pointlessly) perform shadow fighting techniques to point out how kick ass they are. Perhaps to convince us (and themselves) that they're not just, you know, fighting with cards and plastic toys.
Although in the case of Yu-Gi-Oh!, many characters actually are good fighters, which was particularly relevant in the first few volumes of the manga and the Toei anime. Jounouchi is a skilled street fighter who knocks out a trained assassin and keeps up against a Leather Face expy, Honda isn't exactly a wuss either, Kaiba kicks the crap out of a couple of people, Anzu throws some mean punches, Yami Yugi is hinted at being quite capable (particularly in the Toei anime, where he has no troubles slamming his puzzle into the wall or kicking the daylights out of two of Kaiba's mooks who where twice his size (off-screen, sadly) and Yami Bakura wasn't exactly weak either; let's not even start bringing up their past selves, who were all without a doubt trained in combat.
Kenichi: The Mightiest Disciple. Subverted in some characters, like Niijima or the girl who has a crush on Kenichi, but pretty much the whole cast has knowledge of martial arts, even Shigure's mouse.
Naruto is a justified example, considering that most of the story takes place in hidden villages completely organized around training Highly Visible Ninja.
Ikki Tousen, good God. Pretty much every character that gets any amount of screen time can be seen fighting at some point or another (and that's counting the minor ones).
The Dragon Ball series. Everybody from the little old man to the evil bubble gum alien seems to know Kung Fu.
The same goes for many DC universe citizens, but especiallyMetropolis. Expect the invasion of aliens or a terrorist attack from a third-world dictatorship to turn into a pipe-swinging free-for-all in the streets in five seconds flat.
Well, they do live in a world where the very existence of the universe is at stake three, four times a year. Ninjas. Face-huggers. Sometimes even crime. You tend to get a lot of practice in close-quarters combat just walking down the street.
One of the staples of Jackie Chan's films is him playing a kung fu fighting cop. Jackie Chan's opponents tend come from all walks of life, including accountants.
A plot point in the movie Shaolin Soccer: the hero wants to spread Shaolin Kung Fu and points out to a soccer coach how it could be used to improve peoples' lives (like avoiding Banana Peels and parallel parking). After they win a soccer tournament with an entire team of Shaolin monks, the hero gets his wish, and we get a Montage of people using kung fu in their everyday lives. In the English dub, the song that plays in the background is a cover of Kung Fu Fighting by Carl Douglas.
Played with in the 2008 Speed Racer film, as everyone in the Racer family is able to prodigiously defend themselves against enemy racers, ninjas, etc. Most of them somehow know Kung Fu, although Pops doles out a beatdown with Good Old Fisticuffs. The exception is the Racers' mechanic Sparky, who is totally useless in a fight and repeatedly has to be bailed out by his infinitely more skilled companions.
Pops even wears a ring attesting to his wrestling championship fame.
Enter The Dragon ends with a massive kung fu battle. On one side you have Han's army of martial arts students, trained to kill mercilessly with their bare hands. On the other side you have... a bunch of vagrants and runaways, kidnapped from the streets of Hong Kong and freshly released from Han's dungeons. The two sides appear to be about evenly matched.
Chocolate, another Thai martial-arts film from the director of Ong Bak. Everyone on the streets of Bangkok, from warehouse labourers to butchers to gangsters, is a martial artist of some kind (except for the transvestite gangbangers, who use guns). Almost all of them have their ass handed to them by an autisticteenagedgirl.
Undefeatable plays this to the bone. Random women in red dresses that resemble the antagonist's wife strike stances and try to fight, among other characters that have no business knowing martial arts. To be fair, all but the four main characters are terrible at it.
Lampshaded in one episode where Dawn complains that it takes her forever to learn any martial arts whereas all newborn vampires "seem to spend a couple of months at the same tae kwon do school".
Lampshaded in the Season 3 premiere when the Scooby Gang are hunting vampires while Buffy's out of town and encounter a newborn vampire who hands them their asses in this fashion. When Xander, pissed-off, demands to know how the hell he learnt that stuff, Oz recognizes him as a former classmate who used to be captain of the gymnastics team.
Any Power Rangers hero or side character intended to become one later will have mad fight skillz even if there's no indication that they've ever taken a single karate lesson. If they don't have any the very first time the Mooks show up, they will by their second appearance.
Also of note is that a ridiculous number of people in the original seasons were nuts about martial arts, long before Rita attacked. Once the franchise finally moved out of Angel Grove in season 7, this was realistically dropped. However, a couple later seasons had the heroes get caught up in the fight and become Rangers specifically because they had been already been training in Supernatural Martial Arts.
Averted with the original Blue Ranger. Billy didn't have any martial arts skills in his human form at the beginning of the series and even seemed to have trouble with Rita's Putties. Following an episode that had him actually taking lessons from one of the other Ranger's relatives, he started to get better over time.
Hilariously subverted with Green Ranger Ziggy of Power Rangers RPM. Even all the way to the season finale, he's always struggled in a fight (in comparison to his fellow Rangers).
Lovejoy, a British TV series (very!) loosely based on some novels about a conman-cum-antiques-dealer, subverted this one in a scene where Lovejoy's ally of the week, a Japanese man, frightens off a gang of thugs by pretending to know kung fu. After they're gone he explains that everyone just assumes he can kick their butts because he's Asian.
That also sums up the plot of They Call Me Bruce? (1982).
Xena: Warrior Princess. Not only does everyone (outside of the mooks) know Kung-Fu, they know different styles: Karate, Capoeira, Judo, pressure point manipulation — if it's vaguely martial art-like, a Xena character has used it. Yes; in Ancient Greece.
Fully justified. Ancient Greece was, by modern standards, a violent place where swords, spears and unarmed fighting were commonplace, accepted elements of everyday life- yes, even in "gentle", civilized Athens. (Socrates was an ex-soldier). Pankration was a clearly defined martial art complete with strikes, throws, and submission holds, and remains a viable art even in the modern age of Ultimate fighting.
Even more justified as some scholars suggest that kung fu was invented by people who had learned Pankration from Alexander's soldiers during his eastern campaign.
In fact, in ancient Greece, every male had to join the military, so it's entirely expected that they should know how to handle themselves in a fight. They should not, however, know Kung Fu.
Pankration was more like wrestling than a martial art relying on strikes, although it had those too. It was invented by hoplites in case a soldier fell down. In this case, trying to get up would most likely result in getting stabbed, so the alternative was to drag the opponent down on the ground with you and choke him to death. The original Olympics had Pankration as the main event with the top contenders fighting naked. The only moves disallowed are eye gouging, biting, and killing your opponent. The champions were treated as royalty.
In one of JD's daydream sequences in Scrubs, Turk and The Todd had to kung fu fight every other surgeon in the hospital for a briefcase. To the song "Everybody Was Kung Fu Fighting". See it here.
One episode of Charmed had no supernatural enemies whatsoever. Instead the episode's villain was a corrupt District Attorney who was trying to frame his mistress for murder. Towards the end of the episode the mistress confronts the District Attorney and the two of them suddenly engage in a brief kung fu fight completely out of left field.
In the roleplaying game Feng Shui, one of the cardinal rules of combat is that everyone — EVERYONE — knows at least some kung fu. They might not have enough skill for it to register in their stats, but if a character is capable of more motion than your average baby, then they know kung fu.
Except for those who have just the Guns skill combat-wise, like the Killer or the Techie. Those guys just dive around, take cover, and use the Guns and Gunplay Tropes to full effect. Or the Sorcerer, who uses the Sorcery skill to rain all over his enemies' parade. Sometimes literally.
Hong Kong Action Theatre may be a better example of this trope in tabletop games than Feng Shui. In this game, every character, whether they specialize in melee, gunplay, sorcery, or just kicking ass Martial Arts Movie style, knows Kung Fu. You even get to select your character's specific style of Kung Fu upon creation!
One officially listed campaign suggestion for Dungeons & Dragons is to have everyone be a gestalt monk (basically, add in the abilities of the monk class on top of whatever actual class any character has), specifically to evoke this kind of feeling in a campaign.
Exalted loves it's Supernatural Martial Arts and as such:
The companion book "Scroll of the Monk" suggests using this trope liberally and with gusto should one of the PCs be looking for a hidden martial arts master.
Burn Legend, in Shards of the Exalted Dream. The character sheet doesn't even have social or mental stats, and the general assumption is that any NPC of significance is going to be a black belt.
Sidereals (also known as fate ninjas) are all over them. They all, mandatorily start with at least two points in martial arts (Endings Caste start with three and specialises in them). They also have their own whole tier of martial arts, which generally involves beating up concepts of reality and stands above everything else. They also have a unique Background related to having a martial arts teacher.
Fugitive Hunter War On Terror is all about tracking down terrorists around the globe, taking them on in fistfights, and capturing them. Terrorists who, inexplicably, have the same martial arts skills as you do ? including Osama bin Laden.
In Jade Empire, almost every character or enemy seems to have some sort of training in a martial art. Even the lingering spirits of random dead people seem to be capable of martial arts skills as advanced as yours. Makes the sole case of a Distressed Damsel (Fuyao, the girl who you rescue from slavers in Gao the Greater's pirate base) stand out.
The two-person non-lethal takedowns in Deus Ex Human Revolution often begin with the targets attempting to expertly melee Jensen followed by an equally expert counter and finishing move. Said takedowns can be done not just on enemies but also regular NPCs. Which means that you can witness elaborate martial battles not just between Jensen and soldiers, but between Jensen and ordinary civilians or even between Jensen and street prostitutes.
From Assassins Creed II onwards, if you pickpocket anyone and they catch sight of Ezio, the victim will attempt to punch him out. Key word being attempt: It doesn't take many punches from Ezio to put them in their place.
Sleeping Dogs: Most people, including all mooks and many male civlians, know kung fu in Hong Kong. If you hijack a car or start punching people in the street, you may be surprised by the number of people who will at least try to hit back.
Zeno Clash: Everyone you fight is a strangely adept combatant; this is particularly strange, as you are the only one who seems to have gotten any training at all.
Zeno Clash 2: Unlike the first game, a Justification is offered as to why everyone is so good at fighting. The world of Zenozoik is a primitive place, and the people there have no concept of law or justice. The standard dispute resolution method is fighting—much to Golem's exasperation.
Justified in the Whateley Universe stories. At the Whateley Academy, students have to take introductory martial arts ("introductory" in the superpowered sense of the word) or Survival, and those who skip out usually regret it when they discover the Combat Finals at the end of term. So huge numbers of mutants at the school can pull off some aikido or Shaolin kung fu or whatnot. There are over half a dozen teachers whose job is teaching martial arts, in a school of under 600 mutants.
There was an unusual prevalence of combat skilled characters in Survival Of The Fittest V3 and its Pregame, especially since the characters are all, at best, highschoolers. Averted in V2 and V1, mostly, since few characters got opportunities to engage in hand to hand fighting.
The TGWTG Year One Brawl, where every single one of the site's contributors proved to be semi-competent, marginally deadly martial artists. Except for Ma-Ti, who has Heart as his power.
It seems that almost character in Darwins Soldiers is fairly skilled with firearms. Justified in that firearms training and basic marksmanship are mentioned as being mandatory or that the employee in question enjoy recreational shooting.
Sockbaby. In Sockb4by, even Ronnie's next door neighbor is one of the mook squad that attacks him.
One of the initial criticisms of The Batman was that seemingly every villain was an expert hand-to-hand combatant, especially the Joker and the Penguin.
Actually if you think about it, it was only the Joker and the Penguin affected by this, and even their fighting ability was downplayed after their introductory appearances.
Which makes sense if you notice the rarity of guns in that universe.
The Boondocks specifically states that anytime someone throws a chair, everyone will engage in a mass fight. Huey and Uncle Ruckus are apparently gifted martial artists that are good with melee weaponry; in Ruckus' case, this is extremely bizarre (given his terrible health and physical ability, blatantly referred to in previous episodes). Colonel Stinkmeaner started out as a subversion (Huey assumed his blindness made him Daredevil, but it turns out he's just a blind old man who got a lucky shot in), but (ridiculously) returned from Hell a martial arts master, the episode implying that he was trained by Satan himself. This was before his Hateocracy showed up, where they went up against hired bodyguard Bushido Brown
Not to mention that Granddad is a master of Belt-Fu...
In the second season episode "Attack of the Killer Kung-Fu Wolf Bitch", Granddad's internet blind date, Luna, is revealed to know "White Lotus Kung-Fu" and to have won the Kumite (every time the tournament's name is mentioned, there's a little martial arts "hi-yah" noise). Needless to say, eventually Huey tests her skills and is beaten to the floor for his troubles.
For half the fights that break out in Boondocks, participants are shown with inexplicable physical prowess and at least some karate kicks in there.
One episode of Family Guy had the entire family break out into an epic brawl after criticizing each other's faults. Ironically (or maybe not), this brought the family closer together.
Not to mention the multiple chicken fights.
In The Penguins of Madagascar the penguins use violence to solve everything from runaways to making popcorn pop. Skipper, the leader, even says in one episode, "I find reason tedious and boring. We use force."
In a time-travel ep set during the character Jackie's childhood during the 70's, a fight breaks out between present-Jackie, past-Uncle, present-Jade and the Dark Hand, prompting one of the kids to say 'Everybody is Kung-Fu Fighting!'
Avatar The Last Airbender; almost every main-character, both good and evil, knows a version of kung-fu. Most of them know ''superpowered'' kung-fu. Exceptions are Sokka, who functions as the team's Bad Ass Normal (eventually), and a few minor characters, like Yue, Yugoda and the Cabbage Merchant.
This is part of the conscription training for citizens of both Koreas, with Tae Kwon Do instead of Kung Fu as the martial art. In fact, in the case of South Korea, it is more or less an unwritten rule that all children should learn Tae Kwon Do (and only during before middle school, apparently), although it's changing now.