You Have Been Warned

A classic Stock Phrase -- to the point that it became a Predefined Message on The Other Tropes Wiki and here, afterward. It is effectively a punctuation mark upon a description of the terrors or troubles ahead of you, should you continue along the path you have chosen. Usually some helpful and/or knowledgeable individual will list everything the hero (and his friends, if any) will face if they proceed, in either terrifyingly vague terms or excruciating detail. And when the hero decides to go ahead anyway -- well, it's both a way of saying "I Told You So" before anything happens and the verbal equivalent of throwing one's hands up in disgust at the pigheadedness of some people.

Regardless, when you hear someone say this to you, there's only one thing you should do: be very sure you want to continue. If you continue anyway, expect to hear I Warned You in the near future.

You Have Been Warned.

Compare I Warned You, which is more "I Told You So" than "You Don't Want To Do This". See also This Way to Certain Death, which is frequently paired with this trope.

Examples of You Have Been Warned include:

Anime and Manga

Meta-example: When a character asks a question and the reply is the Stock Phrase in Japanese that translates as "Do you really want to know?", the first character Has Been Warned that they might not like the answer.

Fan Works

In Chapter 5 of the Real Person Fic Just Taken, after being told about what happened to Melanie, Aceso had explained how her sister, Iaso, had warned about the interrogation style treatments for anyone with an eating disorder at Olympus Multi-Diagnosis and Treatment Centre. Later, Dave, an orderly, had warned Alife to stay out of any session that Melanie was in. Of course, Alife ignores this, causing a scene that puts Melanie further harm, forcing the usage of medication despite her requests not to do so.

Well, I did warn him to stay out of it. It’s his fault now.

Film

The page image is from the 1939 version of The Wizard of Oz, where the signs warning travelers away from the haunted forest near the Wicked Witch's castle are not content with just stating the dangers, but really quite insistent on the matter.

Literature

Deliberately invoked as Schmuck Bait in the Discworld novel Carpe Jugulum. The Magpyr family lives in Don'tGoNearThe Castle, and the route to the castle is regularly marked with signs such as "Don't take this quickest route to the Castle". According to Igor, it was always full with guests.

Live-Action TV

Get Smart. Repeatedly:

Chief: "Don't tell me that (X)!"
Max: "(X)"
Chief: "I asked you not to tell me that."

Oral Tradition, Folklore, Myths and Legends

Older Than Feudalism: The Bible, specifically 2 Peter 3:17. The Contemporary English Version translation even uses the phrase "you have been warned".

Tabletop Games

The back cover blurb for Violence, Greg Costikyan's darkly parodic roleplaying game of typical Dungeons and Dragons mayhem in the modern world, concludes:

Let’s not mess around. This is not a nice game. It's bloody. It's brutal. It’s dark and evil, with a twisted sense of humour. It uses rude words. "Excessive" is not enough to describe VIOLENCE™. "Bad taste" doesn’t even get close. This is role-playing's answer to the snuff movie. It is not for sensitive people. If you feel you might ever fly into a psychotic rage and kill all your co-workers with an AK47, then put it down and walk away. Please. We don’t need that kind of publicity.
VIOLENCE™ ... does not include dice, pencils, character sheets or anything even vaguely resembling morality or good taste. Consider yourself warned.

Video Games

The highest difficulty level for the Simulation Game The Political Machine 2020 has an icon of a crying eagle and is called "Masochistic". Its flavor text reads "Warning: You will lose. There will be tears. You've been warned."
In an Egyptian-themed level of The Talos Principle there can be found a palm tree with a sign reading "Don't Look Up" nailed to it. Looking up results in a coconut falling from the top of the tree and nailing you in the head. As many times as you care to do it.
River City Girls 2. When the two anti-heroines enter the Witchy Woods, Blair's Villain Song ("Get Off My Lawn") constantly plays in the background, the lyrics telling Misako and Kyoko to go away.
In Fallen London, if you accept the quest "Seeking Mr. Eaten's Name", the game will warn you many times to stop pursuing it. One example:

Why? In God's name, why? What can you possibly hope to gain? Stop now. Before it's too late.

Web Original

TV Tropes: To the point that the counterpart there to This Very Page lists the distractions and dangers of visiting its various namespaces, such as Nightmare Fuel, Darth Wiki and even the Sugar Wiki; it then ended with this:

Are you sure you want to go there? This page—no, this whole site has been known to ruin people's lives, their vocabulary, their spelling, their sense of time, their lives, their perception of reality, their lives, and short-term memory. And their lives. Proceed with caution.

SCP Foundation: If you want to read any of the SCP-001 proposals, you have to click on a link that leads to a page with the following disclaimer:

WARNING: Any non-authorized personnel accessing this file will be immediately terminated through Berryman-Langford memetic kill agent. Scrolling down without proper memetic inoculation will result in immediate cardiac arrest followed by death. YOU HAVE BEEN WARNED."