Any time a nation intentionally annoys a superpower.
Any time someone picks a fight with a soldier or a member of law enforcement, gets slapped around like a training dummy, then acts genuinely surprised that someone who is trained professionally to kick someone's ass just kicked their ass.
Fans at Professional Wrestling shows who jump the rails to attack the wrestlers or interfere in the matches. Professional wrestlers are all either extremely large, extremely muscular, or both. They're also trained and paid to throw their weight around. Not the kind of people you want to mess around with. Individual examples include:
Andre "The Giant" Roussimoff was harassed about his size by four drunks in a bar. Andre attempted to avoid confrontation, but they persisted. Eventually, he chased them out of the bar, and when they locked themselves in their car, he rolled their car over with them in it. Andre was never charged, probably because the police never believed the four drunk guys ranting about an angry giant that knocked their car over.
Davey Boy Smith, the British Bulldog was harassed by a man in a bar who recognized him to the point where the man laid hands on him, Davey Boy Smith (at one time considered the strongest man in professional wrestling) put him in a simple headlock. From which the man was unable to extricate himself, no matter how he screamed or struggled. Sadly, Smith walked him over to the bar's bouncer, said, "Can you take care of this?" and when the bouncer said, "I have it," let go. That's when the idiot tripped over his own feet, fell down, and opened up his skull to the brain on a protruding nail. And sued.
Paul "The Big Show" Wight, whose initial wrestling moniker was "The Giant". 7'2 (or 7'4, depending on whose measuring) and between 450 and 500 pounds, is famous for being one of the fastest and most agile super-heavyweights of the modern era, if not ever. So some drunk in a bar decides to insult him and deliberately try to pick a fight with him so he can later sue. Too bad that everyone on the bar - including the bartender and multiple security cameras - all witnessed Paul try to talk the guy down for a good five to ten minutes, and not respond until he was struck several times. Then he punched the guy once.
Richard Kuklinski told a story of an associate of his who owed money for gambling debts. Kuklinski vouched for him and told the associate that he should make sure to pay up. The associate told Kuklinski that if Kuklinski didn't continue to vouch for him, he would harm Kuklinski's family. Kuklinski is perhaps better known as "The Ice Man", a professional assassin for, among others, the Gambino mafia family. No guesses for how Kuklinski took care of the matter. However, Kuklinksi is widely suspected of having been the teller of tall tales.
Friends of Bruce Lee claim that a man once snuck into Lee's home in order to challenge him to a fight. Supposedly, Lee put the man in the hospital with one kick.
Another (Possibly a retelling of the above story) claims that a paparazzi snuck into Lee's home to snap pictures and terrified his kids in the process, resulting in the most powerful kick Lee ever threw.
Steven Seagal claims that a man came into his dojo in Japan and challenged him to a fight to the death. Initially taking him seriously, Seagal launched a flying kick, only realising once the attack was committed that the man was drunk.
British Royal guards are the guys in the funny uniforms who are renowned to never move or act without reason. Urban legend holds that you can mess with them and they're not supposed to move. That's incorrect. They carry loaded assault rifles with bayonets and are active duty military personnel. Messing with them will provoke a swift reaction. Photos with derpy expressions you can get away with, although even with the "act without reason" part of their conduct it's wise to not be too rude.
Some incidences of animal abuse occur on very powerful animals that could kill the attacker easily, if only they didn't have a My Master, Right or Wrong mentality. Seeing an instance of this is what inspired George Orwell to write Animal Farm - he saw a young boy whipping a horse much larger than he was, and was struck by the contrast.
Pretty straight forward example here. Casey Heynes was being picked on by a kid two-thirds his size. When the smaller kid began throwing some vicious punches, Casey had enough.
Less dramatic examples than the others, but anyone who taunts an admin or mod on an online forum.
Teachers, have fun teasing some of the most influential persons in your career. Ignore the risks of never getting an exam, job or degree.
When a Troll decides it would be funny to antagonize a bunch of expert hackers on their own forum. You can imagine how that ended.
Next time you think you're so anonymous, try it on a forum where I can't see all the guest posters' IP addresses. (troll's computer is wiped clean)
In the same vein, when someone thinks it's a good idea to antagonize a fandom with a major Berserk Button and which is known for its internal drama by pressing that button. All those people fighting with each other over petty issues may well unite to fight the outside troublemaker.
Why are their signs in zoos that say "Don't tease the animals"? Because people who do fit this Trope to a T.
Most animals who have run into a skunk tend to avoid them at all costs, including bears! Still, some dog owners have reported having dogs who just don't get the message, and there are some animals with that same mentality. Pity the dog owner that found out the hard way ... and having to bathe that terrible smell off their pet.
Porcupines and dogs. A golden retriever will yelp and run away after getting a few quills in its nose, having learned a valuable lesson. A pit bull will get pissed, grab and shake the porcupine, getting quills stuck in its mouth, in its eyes and all over its head and neck.
Despite some rather obvious problems with this approach, some would-be thieves still try to rob agun store, police station, or a jailhouse.
A man by the name of Frank "Rocky" Fiegel who lived in Chester, Illinois was known throughout the town for being the local scrapper. One tale mentions that several young men took him out to the woods with the intent of ganging up on him and beating him up. He came back without a scratch while the men out in the woods needed medical attention. To further illustrate this man's fighting ability, he was the inspiration for a certain cartoon character with a noted love for spinach.
Nikolai Valuev is a 7 foot tall, 320 pound professional boxer with a record of 53-2-1. Yet, a 61 year old man STILL decided to cuss out his wife over a parking spot. Needless to say, the first punch literally knocked him several feet through the air.
The attack on Pearl Harbor in World War II, as noted in the entry for Tora! Tora! Tora! above. Yamamoto may or may not have actually said the "sleeping giant" line, but we do know that he mentioned his misgivings regarding this to his superiors:
Yamamoto: In the first six to twelve months of a war with the United States and Great Britain, I will run wild and win victory upon victory. But then, if the war continues after that, I have no expectation of success.
Germany's attack on the Soviet Union (with whom they had a previous nonaggression pact) didn't turn out any better. What makes it this trope is that any idiot should be able to look at population numbers and know that for Germany, losing half a million men out of their army would be a disaster, whereas for the Soviet Union sacrificing one million men to kill half that many Germans would be a victory.
Audie Murphy in Hollywood. Wannabe macho types would take one look at this wiry little five-foot-eight man with the babyface and the soft, high-pitched voice and say: "That's the most decorated American soldier of WWII? I bet I could take him." Murphy had been a scrapper in school and in the Army due to his hot temper, small size and Embarrassing First Name, and practiced boxing and judo in Hollywood. He invariably curbstomped his attackers with anything that was handy, ranging from riding crops to lead pipes to bricks. Eventually he got tired of having to deal with these clowns, and finagled a concealed-carry permit from his friends in the LAPD. After that, he would usually just pull a .45 service pistol on the troublemakers and make them back down without a fight, which saved considerable wear and tear on his knuckles and their faces.
Tim Langdell (Owner and sole employee of Edge Games) made a career out of bullying dragons — he had numerous dubious trademarks on the word Edge and would force settlements out of companies to use the word, using doctored evidence to make it look like he was maintaining the trademarks (and they were thus valid) when he actually wasn't. Amusingly, his downfall came partially from picking on someone his own size — although it was ultimately the biggest, nastiest dragon he tangled with (one Electronic Arts) that humiliated him in court and forced him into a settlement that was very much in their favor (including forcing him to withdraw many of his trademarks), their legal case was based in large part on evidence gathered by indie game developers and enthusiasts after they bullied small independent developer Mobigame, having their title Edge removed from the iPhone App Store and threatening them with legal action if they tried to reinstate it.
John "Totalbiscuit" Bain has had several problems with indie game developers putting copyright strikes against his YouTube channel after he gives their games extremely scathing reviews, only to back down after TB or his fanbase tear them apart. One of them (the makers of Guise of the Wolf) actually threatened to sue, only to back down when Totalbiscuit encouraged them to do so, knowing that no sane prosecutor would willingly take a losing case (as reviews are constitutionally protected) as well as having Polaris' lawyers at his back.
"Contempt of cop," when someone antagonizes or insults a police officer, often causing the officer to respond with force and a "disorderly conduct" or similar charge.
Annoying judges or lawyers, the people who represent and sentence you in court is an extremely stupid move. One girl in California was disrespectful to a judge, so he doubled her bond. When she told him to go fuck himself, he told her to to the County jail for 30 days. Another example is threatening lawyers - the fans of Rangers football team in Scotland now have a very small pool of people prepared to represent them because of their charming habit of threatening lawyers they don't like with nail bombs, which turns the entire Scottish justice system against them. Lawyers stick up for each other when the chips are down, and making trouble for one, or threatening them, is a good way to get them to exercise their nearly unlimited power to teach you a lesson in manners.
North Korea, while having a very large military in personnel, and having the highest percentage of military spending to GDP (25%), they still fall under this trope, since their army is generally poorly fed, equipped with outdated weapons, and spends a lot less on its military than South Korea does (which almost spends as much on its military as North Korea has a GDP). Yet they still have broken the cease fire agreement with the south many times and constantly advocates its wish to crush South Korea and the US. They only get away with it because they are backed by their own dragon, China (and even China's beginning to get sick of putting up with their crap). Their nuclear arsenal make them a very dangerous enemy to South Korea (provided they could successfully launch a nuclear missile, which is questionable). Nevertheless, threats against the United States still fall under this trope.
Burt Reynolds tells a story of meeting Rocky Marciano. Reynolds sized up the former heavyweight champion boxer and thought to himself that he could probably take him. Rocky immediately leaned forward and said, "Don't even think about it!" When Reynolds asked how he knew what he was thinking, Marciano simply replied, "I always know." Apparently Marciano had trouble with people thinking they could best the champ.
Aaron Barr of HB Gary Federal publicly bragged on the Internet about how he was going to take down Anonymous using social engineering, after having done "research" on potential criminals- in reality, mostly innocent people who passively supported them, which pissed Anonymous off to a huge degree. Yes, that Anonymous. It... didn't end well for him. After the resulting digital Curb-Stomp Battle, he was forced to resign in disgrace. Stephen Colbert said it best:
Anyone stupid enough to intentionally piss off Anonymous or doing acts that get their attention will usually not survive the backlash they will receive. The Zetadrug cartel are one of the exceptions (specifically, the Zetas threatened to kill people if Anonymous messed with them) - so in that case, it was one dragon bullying a nastier dragon.
There's an old Brazilian saying that goes like this não se deve cutucar a onça com vara curta (translation: do not poke the jaguar with a short stick) when someone is annoying someone that can easily take you down. The comparison makes completely sense considering the jaguar has the second strongest bite among the mammals.
When this comes to animals, this does not even have to apply to the big, scary ones. Most insects for example offset their size by having extremely painful bites and stings, some of which can even kill.
Angry crowds can be dragons too. Akku Yadav was a criminal who had been committing rape and murder in the Indian city of Chennai for over a decade, and getting away with it due to police corruption. When he was brought into court, he spotted a woman in the crowd he had raped and called her a whore. This utterly enraged the crowd, which consisted of over 200 women, and he was brutally lynched on the spot.
A group of thugs reportedly sized up Chuck Norris, not believing his badassery to be real (memes aside, Chuck Norris is a highly skilled martial artist with multiple black belts, including one in a style he invented himself). When the police showed up a few minutes later, Chuck was leaning amicably against the wall and the thugs' arms were broken so badly the police were afraid to handcuff them lest their injuries become even more severe. That and the cops were laughing themselves sick at the whole situation.
Reportedly, one of the officers asked the injured thugs something like "Do you not know who this man is?" to which they responded "Yeah, we know, but we thought the stuff on TV was fake!"
There are instances of people deliberately provoking powerlifters. Some powerlifters have a stocky build or may look fat, but this is because they operate squarely on Stout Strength. More than a few of them have shown that they have the strength to tell gravity 'no' in regards to upwards of 500 pounds of weight for measurable periods of time. Antagonizing one of these people to the point of physical confrontation is a bad idea, and yet it's happened because someone thought they could 'take the fat guy' and get launched instead.