Deadly Prank

Roy: It was just a joke! We didn't know Mrs. McNulty was allergic to weasels!

—The Order of the Stick

Pulling Practical Jokes on people is all well and good in a comedy—it's part and parcel of the laugh department, and we love watching some pompous ass get taken down a peg or two in some clever and humorous fashion. But in a drama, mystery or horror movie, a practical joke, if it's not played with cruel and malicious intent by cruel and malicious people, has a very high chance of going horribly wrong and ending with somebody getting seriously hurt or even killed as a result of the prank, such as the old guy you meant to give a harmless scare turning out to have a heart condition, or someone cracking their skull after slipping on a banana peel, or any number of other horrible unforeseen consequences.

If you're in a drama, you will most likely have to deal with the fallout, emotional and otherwise, of what you've done, with plenty of Anvilicious Can't Get Away with Nuthin' overtones. And god help you if this happens in a horror movie, as chances are excellent that your victim or one of their loved ones will come after your sorry hide for some very bloody vengeance, even if they have to rise up from the grave in order to do so.

Some Deadly Pranks are meant to end in the other person getting hurt or killed, like the variety of the Prank Date that ends in the victim getting robbed, raped or killed, and such pranks signify that their perpetrators are utter scum who get their amusement from making other people suffer.

If the prankster puts his/her own life at obvious risk by pulling the prank, this is a subtrope of Too Dumb To Live.

Contrast Massive Multiplayer Scam.

Examples of Deadly Prank include:

Anime and Manga

In Rosario + Vampire, Mizore pranks Kurumu into thinking Gin took her virginity. It becomes this trope when it's revealed that hurting a succubus's heart too much can be fatal.

Comic Books

Bobby in Hack Slash gets one of these when a couple of guys put him in a chamber and pretend to gas him. When they try and shut the gas of it fails. He later turns into one of the slashers.

Film

The '80s slasher film Terror Train, starring Jamie Lee Curtis (of course) and David Copperfield (what?), has this as the killer's motivation. A group of sadistic med-school frat boys lead a socially-awkward student where he is told a girl is waiting to have sex with him. Of course, once he pulls off the bed sheet, the "girl" turns out to a dismembered corpse. Naturally, he freaks out and ends up in a mental asylum. Of course, this almost gets them kicked out of school, but surprise-surprise, three years later during a graduation train ride, the frat boys (as well as a wrong place, wrong time David Copperfield) start getting knocked off...
This is the origin of Troma's The Toxic Avenger. Geek Melvin is set on a Prank Date with the The Ditz/The Vamp. After some events that involve a ballet tutu and a sheep, he's laughed out of the gym locker room by what seems like the entire town, and takes a running jump out of the window and into a vat of radioactive waste. Yeah...
Urban Legend's villain was set off by the death of her boyfriend, who was killed in a car accident, the result of the other characters scaring him by putting their flashers on and chasing him, in imitation of an urban legend.
The high school film Jawbreaker features the main characters staging a kidnapping for their friend's birthday. Unfortunately, this goes horribly wrong when the intended victim chokes on the jawbreaker they were using to gag her.
In The Orphanage, Tomas died as a result of this combined with his own refusal to be seen without his mask. However, the standard horror-movie revenge thing is enormously subverted, as yes, his mother did kill all the kids responsible, but no, the disappearance of the protagonist's kid has almost nothing to do with the entire business.
Provides the motivation for the killer in the early 80s slasher film The Burning. It tells the story of a cruel, alcoholic caretaker at a summer camp (nicknamed Cropsy, after the huge garden shears he carries) who falls victim to a prank that went out of control and leaves him horribly burned and disfigured. Following his release from hospital, he returns to his old stomping ground and begins a murder spree. Naturally.
In The Butterfly Effect, Evan and his friend put a stick of dynamite in someone's mailbox to blow it up. A woman carrying a baby happens to come to check for mail at the worst possible moment, and they're both killed when it detonates.
In the movie The House on Sorority Row sorority girls play a prank on their house mother, but it goes wrong and she ends up shot and killed. They hide her body in the pool. Later someone starts killing them. It turns out to be her mentally disabled son she kept in the attic who saw his mother get shot and wanted revenge.
Sorority Row released in October 2009 is a remake of The House on Sorority Row but with a slightly different plot. The Sorority sisters have one of the sisters pretend to die in order to prank a boy. At an abandoned coal mine shaft they pretend they have to look for something to dismember the body. The boy thrusts an object through her body, killing her (he thought she was already dead). They hide the body in the coal mine shaft, but later they get messages on their cell phones from someone saying they know and threaten to report them to the police and then someone starts killing them.
Penn and Teller Get Killed features Penn & Teller one-upping each other with pranks, to the point that when a murderous stalker fan starts trying to kill Penn, he believes that it's just another of Teller's tricks. It turns out that the fan is Penn's prank on Teller, but Teller gets so freaked out that he purchases a gun unbeknownst to Penn and accidentally shoots him just when he's revealing the prank. Teller and everyone else related to the prank kill themselves in grief, and then random people who stumble upon the scene begin shooting themselves in horror as the credits roll.
The Catacombs features a young woman visiting her sister in Paris. The sister invites her to a secret underground rave in the Parisian Catacombs, where the sister's friends get the protagonist drunk on absinthe. Then, the sister is apparently murdered by a psychopath, and the police raid the rave, causing everyone to disperse before the protagonist can get help. The psycho continues to stalk the protagonist, who suffers some injuries, but eventually manages to dispatch the killer with a pickax. She then runs into her sister and the friends. It was all a joke... they just pumped her full of alcohol and put her through Hell for a lark. Then they realize the protagonist (in a failing mental state) killed the "psycho". They start yelling at her... and she's still holding the pickax...
Mean Creek's entire plot focuses around this trope. A shy boy named Sam is getting bullied by a bigger kid at school named George. In retaliation, Sam, his older brother and his two friends and Sam's girlfriend invite George on a canoe ride up a creek, where they intend to steal his pants, push him into the water and make him walk home. They are surprised that the bully actually tries to fit in and be friendly to them, revealing he doesn't have many friends. George's crude behavior though, and his vulgar and violent reaction when he finds out what they intended to do to him, leads to a confrontation where George is knocked into the stream, hits his head on a rock and drowns.
In Zombieland, Bill Murray in Zombie makeup decides to play a prank on Columbus and Little Rock by dressing up as a zombie and trying to scare them. This leads to a very surprised Columbus delivering a blast of buckshot through his chest.
- There's also kind of a potentially Deadly Scam, if you will, when Columbus and Tallahassee are told that Little Rock is infected and that they have to shoot her. Not the best scam to pull on complete strangers who have obviously seen a lot of action and are probably willing to pull the trigger.
Trick 'r Treat plays with this. A group of kids play a prank on the "idiot savant" kid, when they dress as zombies and scare her. She, terrified, falls into a ravine and cracks her head on a big rock. After one of the pranksters, horrified, asks "Is she dead?" she turns out not to be; just badly hurt and still panicking. Then the actual zombies show up and eat the pranksters, the savant pointedly doing nothing to save them.
The Graveyard uses this trope. Lesson being? Don't play pranks in graveyards.
A Deadly Prank is ultimately the cause of Katie Marcum's murder in Mystic River.
Inverted in Doctor X, in which an Explosive Cigar saves the protagonist's life by scaring off his would-be attacker.
The main drive behind When Good Ghouls Go Bad.
Not quite deadly, but the prank in the prologue of Black Sheep combined the the subsequent news of his father's death causes Henry to develop extreme ovinophobia.

Literature

In Stephen King's Carrie, not only did the malicious prank at the prom trigger the title character's deadly telekinetic rampage, it also resulted in the death of Carrie's date Tommy Ross as the bucket of pig's blood hit him upside his head and killed him.
In Stephen King's Needful Things, the main villain is a store owner, who sells everybody what they wish the most for very low prices, but the customers also have to do a prank on someone. Little do they know that those pranks worsen existing grudges between people, and eventually lead to murderous encounters.
This makes up the whole of the plot of the novel Killing Mr Griffin and its derivative movie.
Used in Harry Potter when a sixteen-year-old Sirius Black tricks Snape into going down a tunnel with Lupin in werewolf form at the end. (Snape survives due to the intervention of James Potter). Disturbingly, both Sirius and Lupin refer to it as a practical joke more than thirteen years after the event, and Sirius doesn't seem to receive any punishment for it.
- YMMV on whether Lupin is justifying it. (Sirius definitely is)
In Labyrinths of Echo by Max Frei, the protagonist was informed that now he's able to spit instant-kill magical poison, he will do it if very enraged or afraid, and as such got a status of more or less a human Grim Reaper. He contemplated spitting at one dirty-mouthed guy while in normal mood, but realized such a joke might cause heart failure. So later he spat at an approaching insane cannibal, who in his opinion looked inadequate as a threat, just to scare. And learned that "really afraid" part was optional after all.
In Rex Stout's The League of Frightened Men (1935), the second Nero Wolfe book, the titular league permanently disabled an unpopular fellow college student many years ago in a hazing incident. (They're frightened now because after years of patronizing him, they're panicking at the idea that some sudden deaths among them may be due to his having murdered them, and they can't prove it.)
In Good Omens, when the demon Crowley is being hunted by other demons, he precariously balances a bucket full of water over his office door. A bucket full of holy water. It works.
In Private, after Thomas humiliates Reed in front of the entire Easton Academy campus, Noelle and the rest of the Billings Girls group decide to punish him by kidnapping him as part of a prank. They get him drunk, strip him, shave his head, drive him to a remote area and tie him to the trunk of a tree and leave him there. They intend to drive back after a couple of hours and free him but things do not go to plan when Thomas is then found murdered. This leads to a five book story arc with Reed trying to discover the identity of the killer and clear her current boyfriend's name.
In the Heralds of Valdemar titles, Herald-trainee Talia is nearly killed when some young nobles throw her into an icy river "as a joke"—too bad they added a Pre-Mortem One-Liner to Talia before they threw her in. (It had been foreshadowed that these students might make an attempt on her life on the off-chance one of them would be named heir to the throne.)
The Ninth Circle of the Tour of the Merrimack series begins with a youth dying in a hazing ritual gone wrong.

Live Action TV

Psych has this as the murder in Scary Sherry: Bianca's Toast. The sorority sisters intended to scare off a pledge. However, the casement window she was startled into was unlocked and she fell to her death.
Supernatural has two kids inadvertently summon a real monster while playing a prank in "Hell House." In a later season, childish pranks turn deadly in a small town, with a joy buzzer somehow electrocuting its victim, and a teenage girl scratching a hole through her skull after someone put itching powder on her comb. As it turns out, a little boy in town is developing Reality Warper powers without realizing it, and the joke items are becoming dangerous because he believes they're dangerous.
- Then there's the trickster, who does this on purpose (well, more like not caring if he permanently scars or kills someone and will keep doing it). Made worse by the fact that he's actually an angel under "witness protection" and technically, The Powers That Be allow him and even encourage him into killing people to prove he's "Loki".
Saturday Night Live uses this trope in its "Pranksters" sketch. The eponymous show presents hidden-camera pranks that start off as harmless. Then Christopher Walken's character shows the video of his prank, summed up best with the quote "I pranked him to death with a tire-iron!" Hilarity Ensues.
A parody of this is played up in Scare Tactics, where the scare victims are tricked into going onto a fake reality TV show called "Fear Antics", where they're put under the impression that they're going to pull a huge fright-based prank on someone for the cameras. However, the other participants always rig the stunt so that it looks like it goes horribly wrong, causing the victim to think they've inadvertently seriously injured/killed/got in some other deep trouble the person they were supposed to scare.
- Backfires in one episode, when the prank-victim, confronted by the prankster "killer," grabbed a knife and nearly tore into the prankster.

"OH FUCK, NO NO NO, YOU'RE ON SCARE TACTICS, IT'S A TV SHOW, IT'S A JOKE, YOUR FRIEND SET YOU UP JESUS CHRIST FUCK."

- In one episode, the prank-victim was fooled into thinking he was trapped in a Gas Chamber, and he broke a hole in the wall.
B.J. and Winchester set Sgt. Zale up for one of these in a later episode of M*A*S*H after Zale plays a prank on B.J. involving a fake grenade.
The Masters of Horror episode "We All Scream for Ice Cream" starts with a childhood prank gone deadly wrong.
In the Tales from the Crypt episode "Abra Cadaver" a doctor pulls a prank on his brother, scaring him into a stroke and ruining his medical career. The brother never forgets and gets revenge with another prank years later... killing his brother twice.
- Happens in another episode, "This'll Kill Ya", when an asshole doctor thinks he's been poisoned by one of his colleagues. It turns out that his colleague had tricked him to teach him a lesson, but this isn't revealed until after the doctor kills him as "revenge".
Degrassi the Next Generation: "Time Stands Still Part 1" in which Rick is painted and feathered after winning at a game show contest. He goes home and starts looking at a gun in a box. Then comes Part 2.
There was an episode of Alfred Hitchcock Presents where some guys knocked out their friend and buried him at the beach to humiliate him. Unfortunately, by the time they came back, the high tide had already drowned him.
In one episode of CSI, a woman sneaks a large block of dry ice into a guy's room, so that the CO2 fumes would make him sick. He and a woman that he sleeps with in the room die. She protests that she carefully calculated the amount of CO2 be non-lethal. She didn't anticipate that they'd be sleeping on the floor. Since the fumes are heavier than air, the concentration near the floor was high enough to be lethal.
- And in another, a juror dies in the jury room. Turns out that he was honking off the rest of the jurors with his attitude, and had happened to mention his peanut allergy (loudly and repeatedly if memory serves). One of the others then decided to lace his chili with peanut butter to bring him down a peg or two, not appreciating the potential consequences of his allergic reaction. Mind you, a bee - one of his other allergies - beat her to it.
- In the episode "Pledging Mr Johnson", a pledge is murdered under the cover of a fraternity hazing gone wrong.
- A different episode featured a crusty old poker star who drops dead at the poker table. A number of factors contributed to his death, one of which is that the waitress for the table - annoyed at his extended refusal to tip - put eyedrops into his drink, hoping to give him diarrhea.
- Likewise, there's the time a guy who's still alive, just fully paralyzed, ends up on Doc Robbins' table. He was a used car salesman whose colleagues kept playing pranks on one another to unnerve them/take them away from the sales floor. One of them put snake venom in his coffee, which normally would've just given a really upset stomach... if not for the bleeding ulcer.
In an episode of iCarly, Carly, Freddie and Sam decide to prank Loubert by giving him an exploding muffin basket. They didn't realize it would explode quite so much, dealing serious damage to Loubert, who spends the rest of the episode being tended to by Freddie's mom, which shifts the focus onto a potential romance between the two. By the end, the prank is forgotten and none of the kids receive retribution.
On Cheers the most elaborate prank between Gary and Sam involved Gary getting most of the city of Boston including everyone at Cheers to convince Sam that Gary had been killed by a hologram machine.
On How I Met Your Mother Barney spends a month perfecting an exploding meatball sandwich. It took so long because it had the nasty side effect of decapitating the test dummies.
Buffy the Vampire Slayer; in the episode "Beer Bad", a bartender gives a group of snobbish upperclassmen (and Buffy) cursed beer that physically, mentally, and psychologically changes them into Neanderthals. His intent was to teach them a lesson, telling Xander it only lasts a day; although as Xander himself realizes, a day is more than enough time for them to hurt someone, or themselves. And he's right - while nobody dies, they are almost killed when their antics set a campus building on fire.

Short Film

The short film Spider.

Video Games

The Umgah of Star Control are like this. Their idea of "pranks" include pretending to be another race's gods and ordering them to attack their neighbors, "accidentally" mixing up the Spathi's reply to the Ur-Quan (leading to a great deal of suffering for the Spathi), dropping an asteroid in another race's ocean, etc. It's heavily suggested that the Umgah are simply insane and don't realize the enormity of what they're doing.

Web Comics

A flashback from Something*Positive where Davan's father (when he was a boy) played a joke on a complete jerkass bully in hospital. Turns out the boy had a weak heart, and died from shock.
The incident in The Order of the Stick with the weasel (see page quote)...
In Sandra and Woo mini-arc "Hit Boy" Ye Thuza decided to dress with her kids as superheroes and shoot some blanks and paint at a pair of local drug dealers. Only to see one of them (already high strung) drop with heart attack. Then again, she didn't survive her teen years with guerillas (and still being on "Myanmar’s Most Wanted" list) by thinking slow...
In this SFW page of Oglaf, a girl kissed a frog and instead of turning back into a prince, it turned into a bear.

Web Original

Roommate Alien Prank Goes Bad: Two guys repeatedly scare their roommate Chad with alien sunglasses and hands because Chad hates aliens. Then a real alien shows up.
Everyman HYBRID was started as a parody of Marble Hornets, disguised by having the health/exercise regimen appear to be what is being hijacked by Slender Man; in reality, the in-universe characters are using a prop Slendy placed in rather obvious places. Then the real Slender Man finds out about it, and it seems he is not happy in the slightest. After recent events, the characters are starting to wonder if he would have showed up at some point anyway.
In the Furry Basketball Association, a prank on a player who is addicted to cocaine results in him snorting caffeine instead; the pranksters had no idea it would result in the addict screaming in pain. This trope is ultimately inverted as the player is sent to the hospital, where he's convinced to enter rehab.
From SCP Foundation, SCP-344 is a magical can opener; if used to open a can containing food, it might create a living example of whatever is in the can. For instance, a can of dried apples might cause it to create a living apple tree, while a can of beef might create a living heifer. The file states that a practical joker switched the ordinary can opener in a break room with SCP-334, and a researcher was killed when he tried to open a can of pork. The higher-ups did an investigation, but never found the culprit; afterwards they moved SCP-334 to a vault with better security.
In one episode of RWBY Chibi, Weiss responds to being the victim of a classic bucket-on-the-door prank with her own, only using a frozen bucket. Ruby wasn't killed, but she was knocked out, and the potential for a worse outcome was acknowledged by all but Weiss.
In one Eerie Cuties story, Nina falls victim to a cursed mirror that holds a demon as prisoner - the demon steals her body while trapping her soul in the mirror, and proceeds to play juvenile pranks on the other students, like loosening tops of salt shakers in the cafeteria, tricking a student with a jar or peanut brittle loaded with springy snakes, taking a female student’s bra while she is in the locker room showers and placing it in a freezer, then returning it. Eventually, she ties Tiffany's shoelaces together, an act that results in poor Tiffany impaling herself with her own sword; she survives due to the magical nature of the sword, but spends the rest of the story thinking she's dead, and most of the next story thinking she's been converted into a vampire. It's all pretty traumatic for Tiffany.

Western Animation

In the Halloween Episode of Foster's Home for Imaginary Friends, Bloo pulls the old snake-in-a-can gag on Mr. Herriman. Herriman has a heart attack and dies, and Bloo hastily buries him in the yard. Herriman then comes back from the dead and unleashes a Zombie Apocalypse. No, really! Well, not really. In the end, it all turns out to be a prank pulled on Bloo by the whole house, only it backfires when Bloo unleashes a berserk Mac (hopped up on candy) upon them.
Not quite deadly, but Hey Arnold! has an episode where Arnold accidentally seriously blinds Helga when he takes revenge on her for some pranks she pulled. She gets better, but the rest of the episode is a bizarre Cycle of Revenge. Leads to a funny conversation(taken from memory, so probably not exact):

Arnold: I didn't think it would blind her!
Grampa: Well, what did you think I meant by "it'll release a blinding light"?

South Park: as a joke two Sea Park employees make the boys think that the killer whale is really Willzyx and needs to return to its family in space. It's all fun and games - ending with a big shootout, one of the employees dead ("I still say it was funny!") and the whale dying on the moon, having been shot there by the Mexican Space Agency.
An episode of Pucca has the Vagabond Ninjas prank Sooga Village by releasing termites that eat all the chopsticks, and it all goes downhill from there.
A version of sorts happens in Chowder. After already playing a prank that ruins Mung's catering business, Ms. Endive plays another prank on him, dropping a huge pie on top of him, which turns out to crush him flat. She becomes desperate to keep the accident a secret and eventually decides to leave the country. Turns out that it was all just a prank by Mung to get back at her for all the pranks she did to him.
On The Simpsons Bart pranked Homer on April Fools Day with an extremely shaken can of beer. It sent him to the hospital in a coma, but, more importantly, because of it, we had to suffer through a Clip Show.

Real Life

Four kids got their best friend and pretended to kidnap her and slice her throat. After "slicing" her throat, they revealed it was done for kicks. The girl was not amused, and showed the videotapes to the cops. Now they're in juvie!
Combine this trope with Teens Are Monsters and Bury Your Gays, and you have the story of Tyler Clementi.
A 10 year old boy was at a park playground and when he went down the slide, he felt something sting his rear end. Turns out that an 11 year old boy deliberately planted a razor blade in a hole on the slide and it wound up slicing the victim's bottom. The victim got 30 stiches and is doing fine. The other boy is in trouble obviously.
- Then there are the Urban Legends of kids finding razors and other unpleasant objects inside their candy. Though no poison and very few razor blades have been found in Halloween candy. Although, it is interesting to note that of the few cases where they have found such foreign objects in candy and apples, it's almost always been traced back to either the supposed victim inserting it (for attention for having "found" the booby-trapped item) or a friend or sibling having done it, thinking it to be more or less harmless, akin to a prank call. So, if it weren't that the cases generally have not been deadly (only requiring minor medical attention), this would qualify under a Deadly Prank.
This. A man got drunk and passed out, and his friends stuck a 20-inch eel in his anus. Apparently, it was hungry.
Putting a tack on someone's seat is already pushing the limit of "harmless", but it's not enough for some. They go with crayons and other long, pointy things. While usually not deadly, it can cause irreparable damage to the anus, or the victim could even bleed to death.
In 1999, an Brazilian student by the name of Edison Tsung Chi Hsueh died during a freshmen prank. Seniors hazing the new guys is kind of a tradition, usually with nothing further than giving the wrong information if someone asks where's the bathroom, but other times... Well, Edison was found dead in the university's swimming pool.
One commonly told story, in insistence upon gun safety, is about a teenage girl who hid in her closet with the intention of jumping out and scaring her father. He heard her, but believing her to be out of the house, assumed it was a burglar. When she jumped out, he shot and killed her.
It commonly (and near-universally) agreed upon that screamers (Internet pranks which have the intention of frightening people by popping up suddenly) are considered to be needlessly cruel and in some ways, dangerous. As screamers are often incredibly loud, sudden and frightening when they pop up, many believe that they can cause the elderly or users with heart conditions to have heart attacks, and can even make a person choke if they are in the process of eating food. Regardless of how "deadly" screamers are, they are loathed by Internet users and are rarely found funny, especially if the victim is young and sensitive.
During the Troubled Production of Titanic, disgruntled crew members put PCP on the crew's soup. The main target, James Cameron, vomited upon ingestion, while over 50 people were hospitalized.