Don't tease or mock anyone in a horror film. The monster doesn't like it, and will kill you for it. Not that the monster actually likes the people you mock (it will kill them too). It's just that mocking is the monster's thing. You're butting in.
So don't tease people, don't treat anyone like they're crazy for talking about the monster, and don't play any practical jokes. The last one isn't a Deadly Prank, where someone will get hurt. The monster will just kill you later for pulling one.
Note that this doesn't count if the people you tease laugh with you. That isn't mocking; it's just having fun.
Compare Do Not Taunt Cthulhu, Death by Sex, Death by Materialism, Death by Genre Savviness, Did You Just Flip Off Cthulhu?, Offing the Mouth, Let's Mock the Monsters (when the characters decide to go one step further).
As a Death Trope, all Spoilers will be unmarked ahead. Beware.
- Anacondas: The Hunt for the Blood Orchid:
- The characters are wading through a river. One guy keeps humming the Jaws theme. A girl keeps telling him to stop (instead of just punching him in the face). He's one of the first victims.
- Subverted later when another character is taunting a freshly killed anaconda snake, only to be grabbed by another. Unlike the previous victim, the other characters manage to save him from death at the last minute.
- An aversion occurs in Scream (1996). Two guys pretend to be the killer in school. They don't get killed for this joke, probably because the principal who punished them (and who gets killed later) was even more obnoxious.
- In a Jaws knockoff Blue Demon, some girls are sneaking into a closed beach. The fence is electric, and two of the girls tests it. It's off, but they act as though they're getting electrocuted anyway. They eventually get eaten.
- Jurassic Park has a similar scene, but the victims laugh at that (well, one of them does), so the joker lives to the end (and even through the second sequel).
- The Lost World: Jurassic Park had a guy who taunted a Compsognathus later get eaten by a pack of them, however.
- Averted in Friday the 13th Part 2. Right before Jason really gets started building up his body count, half the characters go into town to go drinking and essentially leave the movie. The practical joker (Ted) goes with them, and survives to the end credits. However, the joker character does indeed go down in parts I (Ned), III (Shelly), IV (Teddy) and VII (Carrie-esque Rich Bitch Melissa).
- Carrie (1976) was pushed over the edge by a particularly malicious prank that was the culmination of all the nasty teasing, taunting, humiliation and pranking done to her by the girls in school. She proceeds to kill just about everyone at the prom before taking her Roaring Rampage of Revenge elsewhere.
- Spoofed in Scary Movie, and later in the third film when Brenda pranks Cindy by saying she watched the killer videotape, and then pretending deaths... and as Cindy is out of the room, "Samara" comes out of the television and kills Brenda (specially because Cindy wasn't believing her cries anymore).
- Steve in Dawn of the Dead (2004). His fault? Bickering with Anna. His punishment? Zombification then bullet through the brain. Riiight...
- Averted in Tremors, where Melvin the prankster manages to survive to the end of the film, and even appears in one of the sequels and the TV series.
- In Freddy vs. Jason, Kia tries to show she's not afraid of Freddy by mocking him to his face. Jason chops her in half from behind.
- A pair of ravers meeting Jason for the first time mock him. This does not end well.
- Anybody who mocks Michael Myers in the Halloween (2007) remake doesn't last very long.
- Barbra's brother in Night of the Living Dead (1968) and its 1990 remake teases her for being scared in the graveyard ("They're coming to get you Barbara..."), and gets killed by a zombie as they ironically end up coming for him first.
- A tv-movie "The Girl Most Likely To..." had a homely, overweight smart girl subject to routine humiliation in college - after she flees one too many and gets in a car wreck, months later she emerges from reconstructive surgery slim and beautiful, and unrecognizable to her former tormentors who now regard her as one of 'them'...she kills them one by one.
- In Unfriended, a girl commits suicide after being cyberbullied. Her spirit proceeds to kill all her friends with the help of social media.
- Buffy the Vampire Slayer lampshaded and then subverted this.
Xander (in a voice like talking to a baby): Who's a wittle fear demon?
Giles: Don't taunt it.
Xander (getting up, looking scared): Why? Can it hurt me?
Giles: No. It's just... tacky, that's all.
- In 2nd Kings chapter 2 from The Bible, a group of young boys made fun of Elisha the prophet by mocking his authority as a God-ordained prophet, telling him, "Go up, you baldy! Go up, you baldy!" (expecting him to go up into heaven like Elijah did). Elisha called a curse on the young boys, and soon after, forty-two boys have been killed by bears.