Hollywood is in love with its own ideas that get repeated in movies and shows, with nobody actually knowing who thought of them first. They get carried on because the audience expects them. There's already a word for the special kind of convenient movie tradition — "trope". For example, "black guy dies first" is a common horror movie trope, which might be explained by the fact most such movies take place at night, where the black skin is difficult to see, so the black guy is offed first to help ease viewers' eye strain.
This text will focus on patently false tropes, such as that one shot knocks a person away, when even a severe head injury might not be enough to kill someone and the deadly shot would most likely make the person collapse on the spot like a sack. Anyway, here are the most unrealistic tropes Hollywood has ever put out.
A grenade pin takes quite a bit of force to take out; doing this with your teeth can break a tooth clean off. It looks cool because it lets our heroes show their pearly whites but that's about it.
Hollywood movies depict the US-Mexico border as a magical line that gives criminals absolute immunity from US prosecution. In reality, the US has had an extradition treaty with Mexico since 11. December 1861, signed by Abraham Lincoln. Any US criminals fleeing to Mexico simply get picked up by the Federales, who deliver them to their US colleagues and presumably high-five one another, laughing at yet another stupid criminal who believed the Hollywood drivel.
I actually think this trope is promoted on purpose in Hollywood movies, since it makes the would-be criminals much more vulnerable to capture as they believe they can do the crime and flee to Mexico, where they'll be free.
In movies, people get shot or stabbed 1, 2, 3 times and collapse immediately, staying motionless. This looks cool in movies because the extras who play the henchman are neatly moved out of the frame and the viewer's perception. In reality, well, it's much messier than that.
People who are severely wounded but not critically injured enter what's known as "agony", which TheFreeDictionary.com defines as "a violent, intense struggle, especially the struggle that precedes death". The origin of the word is Greek agonia, which means "a struggle for victory (in wrestling, etc.)", as defined by EtymOnline.com.
In essence, people with such wounds go through severe pain and struggle that can last for hours before dying. Grown men cry for mommy, shout, scream, gasp for air, vomit, defecate, urinate or do all of those at the same time. This can be so unsettling to witness that the French invented coup de grace, which means "stroke of grace; the merciful death-blow that ends another's suffering", again as defined by EtymOnline.com.
Prior to agony, there's a massive rush of adrenaline that can make the wounded person 20 times stronger than they normally are, allowing them to overcome pain and blood loss to strike back at the attacker. This is why the police is taught to shoot until the target stops moving rather than wound and arrest it; a wounded criminal is at his most dangerous.
Even shooting someone in the head isn't a guaranteed kill. People can survive horrific, tremendous injuries and stay alive for hours. You can read the case of Phineas Gage for yourself.
Hollywood presents sword fights as dramatic dances where swords clash with a TING and sparks fly but that's not how they went. In samurai fights, katanas were often made from crappy metal that would shatter the first time it touched another blade or a piece of metal armor. So, a samurai would aim to instantly win the battle with neat slices and precise stabs, hiding his katana for as long as possible.
A katana master aims at a weak spot, such as the webbing between the thumb and the index finger or the neck. Watch a master swordsman explain this in a video found here (3,502 KB, .WEBM, 1m46s). He pretends to do a Hollywood sword clash and you can see how ridiculous it looks; it's when you use a sword as a bat that you start wildly swinging with it instead of neatly cutting. My guess is that many Hollywood writers are totally gay and have never been in a fight, so they write sword fights as gay ballet dances with a sword.
Other types of swords could be long and heavy, making them more likely to survive the clash with metal but very difficult to swing around for a longer period of time. In essence, sword fights where blades clash look cool because the two swordsmen are in the same shot and they can exchange one-liners with steel between them, which looks great but is unrealistic. Against multiple opponents, an experienced swordsman would just — run away.
This is related to the unrealistic way people die in Hollywood movies I mentioned above. Since henchmen die offscreen and are out of our consciousness, it's presumed that the protagonist forgets about them too. One of Austin Powers movies actually jokes about this with a protracted scene where a killed henchmen's family grieves for him, making the viewer realize they are people too, albeit evil.
In the real world, the protagonist would experience an intense emotional disturbance that would require psychological assistance. Killing 50 people would also cause at least 50 times the grief. I'm not kidding and this isn't an exaggeration; seeing someone die would be very painful and would most certainly impact our protagonist in whatever role he was in. Hollywood uses this unrealistic trope because, again, gay ballerina script writers.
Filming on location is done by asking for a permit from the city council, which then typically redirects traffic. The streets are cleared, allowing our protagonists to roll in and pick their parking spot, when in reality they'd be struggling to elbow their way through foot traffic, let alone the mass of motorized vehicles.
Tenants from nearby buildings are usually thrilled a motion picture is being filmed in their view but then realize — it takes 4–6 hours to film trite scenes, such as the protagonist getting out of the car. During that time, the actors mindlessly repeat the same actions and the same lines until the director is happy with the result. In short, everything you see in a mainstream movie is completely unrealistic, down to parking.
In movies, a protagonist can leap away from the explosion and remain perfectly unharmed, with their person remaining untouched. In reality, it's most often the invisible shockwave that kills, not the flame.
We are surrounded by air, which has its weight, hence the "air pressure" item in weather forecasts. You can imagine it like stacks of tiny bricks that we also breathe in. They're everywhere around us but also on top of us. You feel them as wind when they move or when you move. When something explodes, the force of the explosion gives tremendous power to the wind.
A protagonist standing near an explosion is like being hit by trillions of tiny bricks moving 500 kilometers an hour. The wind would normally move around the protagonist but now it smashes into him like a shotgun blast, with the effect being the same — internal and external injury. Ear drums can get ruptured and the lungs can implode, with the protagonist tossed around like a ragdoll.
A movie shows sleeping darts or sleeping gas? They are going to work instantly and without fail. In reality, a median salary of the doctor dedicated to putting people to sleep (anesthesiologist) is $400k a year, comparable to the lower third of brain surgeons' salary. It's that high for a reason — he can easily kill someone. There's a reason Shakespeare said:
To die, to sleep; To sleep: perchance to dream: ay, there's the rub;
Death is sleep from which one never recovers and the job of anestesiologist is to keep you on this side of sleep, where you can recover. This means taking into account the patient's weight, age, sex, allergies, pre-existing conditions, state of mind and myriad other factors that allow for minimal use of anesthetics without harm. In short, the sleeping darts/gas in the movies would either do nothing or outright kill the people they are used on.