In Trading Places the Duke Brothers' are the architects of their own demise. The two "guinea pigs" they choose for their 'experiment' wind up figuring out what's happening and hatching their own plot. The same former guinea pigs use the Dukes' own orange juice market plot against them. Even the hooker they got to help ruin Winthorpe's life and the butler they drafted into their plan wind up playing small roles in bringing them down. Geez, they'd have gotten off easier by just being honest businessmen.
In any given Marx Brothers film any dialogue between the two resident Pungeon Masters was likely to end with the quick-witted Chico getting the better of the exasperated Groucho by turning his own wordplay against him.
Aliens: the Corrupt Corporate Executive who ordered the colony to acquire the alien eggs (and thereby caused all of their deaths) was eventually killed by the aliens himself.
The film Merlin has Mab. She created Merlin (half-human, half-fae) to preserve the old ways. But, her cruel actions such as killing his mother and imprisoning a lady he loved, made him instead want to destroy the old ways. When he succeeds, Mab disappears because Gods Need Prayer Badly.
In Dumb and Dumber, an enemy poses as a friendly hitchhiker, intending to drop pellets of rat poison into Harry and Lloyd's food. But before he can succeed in this, he needs first aid when his ulcer flairs up (which was induced by Harry and Lloyd's own practical joking). Harry and Lloyd try to administer his emergency pills, but they mistake the pellets of poison for the ulcer medication, and feed him his own rat poison instead.
In Stealth, a medic attempts to inject an initially unsuspecting Ben (Josh Lucas) with 'pain relief' medicine (actually poison). Ben politely refuses, but the medic's stubborn insistence clues Ben in that something is wrong and a struggle ensues. The medic ends up being stuck with the needle himself and dies, showing Ben what the medic was trying to do (not that it wasn't fairly obvious).
This moment in itself leads into Ben's commander being hoisted by his own petard. In trying to cover his tracks by having Ben killed and failing, his duplicity is revealed to his superiors by Ben and he is relieved of command. Then he takes a bullet rather than face court martial.
In Who Framed Roger Rabbit?, after Judge Doom reveals himself to be a toon, he meets his end by getting sprayed with "Dip," a toon-killing cocktail of paint thinners that he himself created. (Given how often he used the stuff, without ever considering that this might happen, it might qualify as Stupid Evil.)
In Dream House, Jack Patterson tries to kill Will and Ann in a house fire. It does not end well for him.
General fate of James Bond's adversaries. Some examples: Doctor No's metal hands made it impossible for him to climb to safety (admittedly, he would have even more of a hard time without any hands at all. On the other hand, he lost his hands from his work with nuclear reactors in the first place), Oddjob was electrocuted through his steel-bladed hat, Goldfinger was sucked out of his own depressurizing jet (also qualifies as an I Warned You, as Bond told him how dangerous firing a gun on a plane was), Trevelyan was crushed by his own evil satellite dish, Carver got shredded by his own giant drill, Renard was skewered by a rod of plutonium with which he was trying to blow up a submarine, Baron Samedi is knocked into the casket full of poisonous snakes into which he was intending to sacrifice Solitaire, etc.
In Moonraker, James Bond kills a knife-throwing assassin by throwing one of the knives back at him.
Bonus points in Diamonds Are Forever when Bond hoists Mr. Wint with his own petard by sticking it onto him and throwing him into the drink. He's blown sky-high before he hits the water. His boyfriend and partner-in-crime Mr. Kidd is the victim of a two-fer—not only was he burned alive when Tiffany Case splashed him with a claret as he approached Bond with flaming shish-kabobs, earlier in the film he had himself tried to burn Bond alive (with the assistance of Mr. Wint).
In the movie Tucker & Dale Vs. Evil, almost every single death is the result of one of these, such as the one person who is intent on killing with a spear ramming himself and said spear into the earth — while holding it. Too bad the spear was pointy on both sides.
In Golden Army, Mr.Wink dies after launching his Rocket Punch into a griding machine. Hellboy even states before "I wouldn't do that" and after that happened "Whoa. Told ya."
Nearly occurs in Iron Man, where the shrapnel that forces Tony Stark to wear his electromagnet comes from a Stark Industries missile used by terrorists. Obadiah Stane's Iron Monger suit was also reverse-engineered from the remains of Tony's first suit.
Stane being killed by the same device he decried as useful only for "publicity."
In the sequel, lots of Hammeroids get blasted out of the air by fire from their own. Also defied, according to the novelisation, as Ivan Vanko specifically constructs his armour so that in case of a mishap (which incidentally doesn't happen) he won't cut himself with his whips.
In Super Mario Bros., Mario and Luigi use Koopa's own de-evolution guns against him, turning him into a tyrannosaurus. Then they blast him a second time, turning him into primeval slime.
Tank Girl. Kesslee had a device that drained a person's blood from their body, killing them, and purified it into drinkable water. He used it to kill one of his subordinates, and at the end Tank Girl used one to kill him.
Doc Savage: The Man of Bronze. The Indian who had acted as Captain Seas' assassin by using the Green Death (created from the venom of poisonous snakes) falls into the pit holding the snakes and is bitten repeatedly, killing him.
At the climax of GMK, Godzilla explodes after his own nuclear breath backfires and instead tears him open from the inside out. Somewhat a subverted example in that Godzilla isn't killed but instead reduced to a disembodied yet still-beating heart.
In Godzilla Final Wars, Gigan fires two spinning disks from his chest at Mothra, who dodges it. Gigan then sets Mothra ablaze with his laser beam. As Mothra is burning, Gigan turns around to savor his victory, only to have the two spinning disks come back and decapitate him.
In The Pink Panther Strikes Again, Former Chief Inspector Dreyfus is killed when his Bavarian castle is disintegrated by his own doomsday weapon. It was supposed to be fired at England, but Clouseau hoist himself into the castle with a conveniently placed catapult. He proceeds to land on the doomsday machine, causing it to swivel around and hit Dreyfus instead, who has his legs disintegrated. Then the doomsday device overloads and starts to dissolve the rest of the castle. The last thing we see of Dreyfus is him slowly vanishing while playing the organ that any self-respecting villain must have in his Bavarian castle hideout.
In Perfume, Grenouille ends his own life by dumping his perfect perfume over his head, causing a nearby crowd to become overwhelmed by the concentrated beauty and devour him.
In the first Transformers live action movie, the Decepticon Frenzy is killed by one of many CD like 'throwing stars' which he himself fired. The thing arced in mid-air and came right back at him.
Starscream's Chronic Backstabbing Disorder comes back to bite him in his shiny, metal ass terminally this time in Transformers: The Movie when he dumps the badly damaged Megatron out into space. This puts Megatron in a position to be found by Unicron and reformatted into Galvatron. Naturally, Galvatron decides to test his new weapons out on Starscream.
In Spider-Man, The Green Goblin is stabbed in the chest by his own glider after trying to use it to kill Spider-Man (Spider-Man senses it, and quickly gets out of the way). This led the Goblin's son to believe Spider-Man killed his father.
In Bride of the Monster, Dr. Eric Vornoff is killed by his own giant octopus. "He tampered in God's domain."
Ghost Rider's Penance Stare allows him to burn the pain of all the people someone has hurt into that person's soul. The film's villain, a demon, has no soul and is thus immune. Near the end, he takes on the power of 1000 evil human souls to start the apocalypse. Guess what happens.
Jurassic Park uses this; create prehistoric monsters and there is a good chance they'll kill you. It is played better in the book and the dinosaurs aren't created as weapons but for entertainment but it otherwise fits the trope.
Rather literal in Law Abiding Citizen. Clyde is about to activate the bomb he set up in city hall. Nick tries to talk him out of it. He activates it anyway, and Nick leaves him in his cell and locks the door as Clyde realizes the bomb is now in the cell with him. He accepts having finally been outplayed and sits on the bomb as it goes off.
In Disney's Tarzan, Clayton repeatedly tries to slash Tarzan with his machete. Unfortunately for Clayton, the two of them are fighting in a thick jungle, where Clayton cuts just the right vines to accidentally hang himself.
In Edge of Darkness, Craven gains a measure of symbolic revenge when he forces Bennett, the man who ordered the radioactive thallium poisoning of both Craven and his daughter Elle, to drink a jar filled with thallium-tainted milk.
In Traitor, the Deep Cover Agent protagonist Samir is unable to break his cover by giving the suicide bombers that are planning to blow up busses in the United States fake equipment. His solution? He arranged for them all to be on the same bus, so that they only managed to blow each other up.
Kinda sucks for the bus driver, though.
In Resident Evil: Afterlife, Albert Wesker escapes from the ship in a helicopter, then triggers the ship's self-destruct device, only to find that Alice found the bomb earlier and stashed it on the helicopter.
A literal example of this trope occurs in The Lord of the Rings: The Two Towers, where the torch-bearing orc clearly didn't make it out of the explosion place. Also many orcs were crushed by flying boulders, not that this stopped the others much.
The director's cut also gives us a straight example: the dam that Ents break to flood Isengard was recently constructed by Saruman to speed up weapon production. It was also said production that made felling that many trees necessary, giving the Ents a reason to attack in the first place.
There's also one in Return of the King, near the very end of it. The Ring's final defense is irresistible allure, ensuring that even if it reaches Mt. Doom's flames, the only place on Middle Earth where it can be destroyed, its bearer will bend to its will and keep it. However, this becomes its downfall when after Frodo reaches Mt. Doom and succumbs to the Ring's power, Gollum, who the Ring had possessed and brainwashed for centuries and who had followed the Hobbits all the way there, fights furiously with Frodo to get the Ring back. He wins, but their fight pushes them both over the cliff, and while Frodo manages to hang on, Gollum clings only to the ring as he falls into the lava, sealing Sauron's fate.
Flash Gordon. At the end Ming is impaled on the nose cone of one of his own war rockets.
For those who've never seen the movie, Robocop had a fourth hidden directive that prevented him from arresting any senior member of OCP. The one who put it in there, Dick Jones, was also the guy who helped supply the guys who killed Murphy, the man who became Robocop. First time he confronts Dick, it activates, leaving Robocop helpless. The second time, Dick makes the mistake of holding the Old Man hostage, who fires Dick. The rest is history.
In the sequel, Faxx shuts off Cain's life support and uses his brain to create Robocop 2. Later, Cain goes on a rampage when OCP unveils him, and Faxx becomes OCP's scapegoat. Cain himself is defeated when Lewis offers him a canister of his own drug Nuke, and Robocop takes advantage of the distraction to kill Cain.
The Terminator series is a prime example of this trope. We created the Skynet system, and right after it comes online it tries to eradicate us by implementing an all out nuclear war.
Batman Returns has the Penguin getting this in spades. When he appears to have the race for Mayor of Gotham City in the bag, Bruce Wayne and Alfred broadcast his previous rants directed at Batman over the loudspeakers during his speech, which include such gems as "I played this stinking city like a harp from hell!" Penguin's Villain with Good Publicity status goes bye-bye, and the eggs and tomatoes are broken out. Later, after his plot to kill all the first-born sons of Gotham is foiled, Penguin straps rockets to his hundreds (thousands?) of penguins in order to destroy the city. Alfred is able to jam the signal used to control them, sending them off to follow a new beacon. When Batman arrives at his Elaborate Underground Base, Penguin wields a sword-umbrella, only for Batman to simply pull out a small remote control with a blinking red button. His eyes shift from the control, to something on the opposite side of the screen. Penguin does likewise, and sees his entire penguin army. He snaps (further than he already had) and is able to take the controller and press the button. The rockets launch, destroying what remains of the park, but also releasing a swarm of bats from the Batski which immediately descend upon the Penguin (a double Hoist By His Own Petard when you remember that he used a similar swarm of bats released by an umbrella in order to send the Ice Princess off a building and kill her, framing Batman for the whole thing). He stumbles backwards, through the ceiling glass, and into the icy polluted water.
Max Shreck, the other major villain, after receiving a Humiliation Conga of his own for his manipulation and betrayal of the above villain, is eventually electrocuted by a power overload to the Arctic World park (presumably coming from the power plant that he had been doing a lot of his evil doings for), with the Kiss of Death delivered by none other than Catwoman, whose alter ego (Selina Kyle) he had been treating like shit through most of the movie. Turns out that one really can have too much power.
In The Pelican Brief, a hitman who had previously planted a car bomb rigs another car in a second attempt to kill the heroine. Luckily, when the car has engine trouble, she recognizes the sound from the previous incident and gets out of the car to flee. The villain attempts to run her down in his own car, but loses control and crashes. Ironically, the impact alone would probably have been enough to kill him, but the car he crashed into? The very one that he rigged to explode. KABOOM.
Towards the end of Popeye, Bluto, who is already winning the fight against Popeye, decides to rub it in by shoving spinach down Popeye's throat *
Yes, in this adaptation Popeye hates spinach, as he did in the original comics actually
. The spinach gives Popeye the strength to win the fight.
In the climax of Strange Days, protagonist Lenny Nero, after getting stabbed in the back by his former best friend Max, ends up clinging for dear life to balcony railing 22 stories above the streets of Los Angeles, with Max dangling from his necktie hoping to take Lenny down with him. Lenny proceeds to pull the still-stuck knife out of his back and use it to cut his tie off, sending Max plummeting to his death.
Bo Catlett imagines how easy it would be to kill Chili if he just had Bear loosen some of the screws on the railing of his deck, which overlooked a cliff. When the eventual showdown happens at Cat's place, he's surprised to learn Bear actually did loosen them.
Subverted in L: change the WorLd, in that K is perfectly willing to die from the virus she created so long as it achieves her goal of ridding the world of humanity. L doesn't let her.
Non-Fatal version appears in Daredevil, when Matt Murdock's partner Foggy puts some stuff in Matt's coffee as a practical joke. The moment Foggy's head is turned, looking at Elektra, Matt switches their coffees, giving Foggy a taste of his own medicine.
At the end of Dirty Pretty Things, the villain, who runs an illegal organ harvesting operation that preys on desperate illegal immigrants, has the tables turned on him by the heroes, who knock him out and steal his kidney.
Pirates of the Caribbean: In At World's End, Barbossa not only cites the code at the gathering of the Brethren Court, but calls on Captain Teague to enforce it, all to avoid fighting Beckett. Jack's motion for the Court to fight won't be entertained because only the elected Pirate King can declare war, and there's no King because a Pirate Lord will always only vote for himself. So Jack calls for an election, lets everyone else vote for themselves, then throws his support behind Elisabeth, who's gung-ho for bringing war on Beckett. Now Barbossa has to go to fight Beckett, since he not only cited the rule that says Elizabeth can declare war, but called on Teague as well. He's got a better chance of surviving a war than a fight with Teague.
Lord Shen in Kung Fu Panda 2 invents cannons, which he uses to kill some of the best kung fu masters in China and plans to conquer all of the land. Po manages to find inner peace and masters the technique for catching raindrops without breaking them, which he uses to catch cannonballs and throw them back. Thus Shen's entire armada gets destroyed by their own weapons. He is killed when he tries to kill Po with his knives and accidentally cuts a rope that holds his biggest cannon, which falls on him.
In the original 1960's Ocean's 11, Danny Ocean's team decides to hide the stolen cash in Bergdorf's coffin. The plan was to wait until it was shipped to San Francisco for the funeral and buried, after which they would retrieve the money. This went quite wrong when his widow, who had not been informed of this, decides to have the funeral there in Las Vegas... and the money then gets burned with him.
In Muppet Treasure Island, the first step of Silver's planned mutiny is convincing First Mate Mr Arrow to leave the ship in a leaky lifeboat, causing the rest of the crew to assume he drowned. When the plan fails and Silver winds up in the brig, he escapes and flees the ship... in a lifeboat which later turns out to be incredibly leaky.
Harry Potter And The Deathly HallowsPart 2 has one involving Snape. He invented Sectumsempra, a spell used for emulating the effect of a sword. Guess exactly which throat Voldemort slices with it? (In the book, Nagini is used instead.)
In Medium Raw: Night of the Wolf, the Wolf removes his armor, and his knife gloves, to climb into a vent and grab the girl. This allows Johnny to grab the gloves, and stab him several times, killing him.
At the end of Snow White and the Seven Dwarfs, the Evil Queen (disguised as the Witch) actually threatens to kill the seven dwarfs by crushing them with a boulder after they've discovered that she actually "killed" Snow White with a poisoned apple and had her cornered at a cliff. Just right before she dislodges the boulder, the Queen is immediately hit by lightning, and tumbles off the edge. Shortly afterwards, her own boulder falls off the same cliff in the same direction as the Queen.
In Mirror, Mirror, Snow White tricks the Queen into eating her own poisoned apple.
In The Hunchback of Notre Dame Frollo, while trying to kill the heroes, keeps hacking the stone gargoyles they are clinging to with a sword. The circumstances conspire so that he has to use one of the gargoyles for support, but the cleaved stone breaks under his weight and he plunges to his death.
In Prometheus the Engineer's own bioweapon is what kills him in the end. Though, Shaw stuck it on him making it a borderline case.
In the 1997 film version of Prince Valiant, Morgan le Fay tries to blow sleep dust into Princess Ilene, but Ilene sneezes, which blows the dust back at Morgan. She gets drowsy and falls to her death. Later, Ilene knocks a mook who was wielding a primitive flamethrower into a vat of oil, with predictable results.
In Tangled, Gothel knocks aside her own basket in her haste to avoid the search parties. If she hadn't, it would never have been found.
Flynn's attempt to scare Rapunzel back to her tower, with the Snuggly Duckling, backfires badly when the thugs there realize they can turn him in for the reward. Only Rapunzel's intervention saves him.
In "The Adventures of Rocky and Bullwinkle," Fearless Leader (Robert De Niro), Boris (Jason Alexander) and Natasha (Rene Russo) are de-generated by their own CDI (Computer De-Generating Imagery) which they attempted to use on Rocky and Bullwinkle over the course of the movie. They are transformed back into cartoons and are sent into the internet "where they were heard from no more."
All of the antagonist fighters in Mortal Kombat is killed off by something of their own.
Johnny Cage kills Scorpion with a spear and shield from several of Scorpion's previous victims, with the saw-bladed shield being used to slice off part of his skull.
When Liu Kang is fighting Sub-Zero, Sub ends up creating an ice field that would freeze anyone who passes through it. Liu Kang finds a bucket of water and launches the water at Sub-Zero, being impaled by the resulting large icicle that is formed.
In the final fight between Liu Kang and Shang Tsung, Shang ends up rising a set of spikes on the floor, intending on sending Liu onto them. Liu turns things around and combos him right into the spikes.
In Wreck It Ralph, King Candy has this inflicted on him twice. The first time, he grapples with Vanellope as he attempts to kill her. Her glitching ends up revealing the truth - that he was the thought-dead racer Turbo. The second time, after fusing with a Cy-Bug, he became drawn into the Diet Cola Beacon through the Cy-Bug's programming, and is destroyed by the hot soda.
In The Avengers, Loki's sceptre, has, unknown to Loki himself, been turned into the kill-switch for the portal spewing his army of Chitauri above Manhattan.
In The Black Cauldron, the Horned King spends the entire movie trying to get his hands on the Black Cauldron, an Artifact of Doom that can create an army of invincible undead warriors out of corpses. Gurgi's sacrifice near the end of the movie causes the Cauldron-born to die. The Horned King, who was pushed near it by Taran, realizes to his horror that the Cauldron is drawing him into it. The Cauldron reduces the Horned King to dust as it sucks him in and brings the castle down with him.
Debbie Jellinsky of Addams Family Values gets hers big time when she rounds up the entire family (with the exception of the new baby, Pubert) and puts them all in electric chairs. Pubert, after taking a very improbable trip to the sky, lands in the middle of the basement where Debbie is carrying out her plan and connects two frayed cords just as she throws the switch, which proves to short-circuit her plans as she is electrocuted instead.
In Death Race, Jason Statham's character is imprisoned and forced to participate in the titular event in order to get a "get out of jail free" card. However, the Warden is not willing to let anyone out of prison, especially since the Frankenstein (whom he impersonates for the public) is the most popular racer of all. So she has her guards put a bomb in his car. When Frankenstein starts to win, she has her people detonate the device. Cue the pit crew laughing as the light on the disarmed device turns on with nothing happening. As the lead mechanic puts it, "Nobody fucks with my cars!" At the end, the Warden receives a package. She eagerly opens it, only to find out it's the same (rearmed) bomb. Cue the view from outside her office, as the building is engulfed in an explosion, as the same mechanic looks on.
Steve Gray the antagonist of The Incredible Burt Wonderstone is a particularly extreme example in that the heroes have nothing whatsover to do with his downfall. He instead manages to give himself permanent brain damage doing an idiotic trick (drilling into his skull live on stage.)
In Deep Rising, Simon Canton hired mercenaries/pirates to scuttle his luxury cruise liner and sink it with torpedoes so he could collect the insurance money. He meets his demise when the boat carrying the torpedoes (all of which had been armed previously in the film) collides into the ocean liner...with him on it and helpless to change its preprogrammed course.
More of a "Hoist By Their Own Petard" version in G.I. Joe: The Rise of Cobra; Duke activates the tracking beacon so the Joes can find Destro's base, just like Destro did so the Baroness' strike team could find the pit.
At the end of the first Wishmaster film, the Djinn defeats himself by granting a time-altering wish that, as he realizes too late, means he was never released from his prison to grant the wishes in the first place.