Unhand Them, Villain!

Batman: Let her go!
Joker: (Beat) Very poor choice of words.

—The Dark Knight

So, the villain has taken a hostage, and to make sure the hero understands that this is serious, the villain is holding the hostage off a roof, or over some other height. Usually, in this case, the villain just has one simple, quick request: they want the code, or the MacGuffin, or the hero's surrender. The hero gives in to the demand. And then says something along the lines of "Now let him/her go!".

Poor choice of words, it turns out, because just this once, the villain is going to comply. Immediately and literally. They let go, and the hostage goes plummeting towards whatever they were being held over.

This happens so reliably that asking a villain to let a dangling hostage go, without being very specific, probably qualifies you as Genre Blind. Even so, this trope is almost always played completely straight. We can only conclude that the sight of a hostage held in the air is the hero's cue to grab the Idiot Ball. Typically, the hostage will survive, but it may require a very well timed Big Damn Heroes moment, or just plain luck.

Variations can occur, as particularly cunning villains may find other, less obvious ways to turn a demand that a hostage be released into a request to kill them. Antiheroes have their own special variation, where they hold a bad guy over a ledge to get information, and then, when the bad guy demands he be let go... well, you know the rest. Sometimes someone's plea to let them go starts at a survivable drop and quickly turns negatory once they get higher up.

This can be a type of Literal Cliff Hanger. For pretty much the exact opposite trope, see Take My Hand. The extremely literal version of a villain complying with You Said You Would Let Them Go.

Examples of Unhand Them, Villain! include:

Anime and Manga

Done by Creed in the Black Cat manga. When Chronos came to destroy the Apostles of the Stars and rescue Rinslet, Creed took her hostage and told Naizer to face the Werewolf alone. Naizer requested that Creed let her go if he wins, to which Creed agrees. After Naizer defeats the Werewolf, he tells Creed to keep his promise. Creed keeps his promise, literally, and drops Rinslet off of the tower.
On The Ocean Group's dub of Dragonball Z, after Dodoria pleads with Vegeta to let him go, he agrees to let him go... to another dimension! Basically saiyan slang for killing him.
- Also done in the original series, in a much more straightforward way. When Piccolo is confronting the king of East City on his airplane, he grabs the king's first mate and holds him over the edge. The king demands that Piccolo let him go, and Piccolo does just that, letting the man fall to his death.

Comic Books

Played with by Doctor Doom in the "Unthinkable" arc of Fantastic Four. Doom is holding Franklin hostage in hell, and holding the arm of Valeria. He promises to let Sue's child go if she'll do what he wants, and when she acquiesces, he releases Valeria's arm. She's in no immediate danger, though. The current author was deconstructing Doom's Noble Demon habits.
Molly from Runaways shows an awareness of this trope. When a giant is holding one of her friends she follows the demand that the giant put the friend down with "And not, like, down your throat."

Film

The Dark Knight: The Joker does this with Rachel. Luckily it wasn't a sheer drop he was holding her over, so Batman has time to save her.
The Anti-Heroic variety showed up in Commando, after the fact:

Cindy: What happened to Sully [the mook]?
Matrix: I let him go. dropped him off a cliff

Made a brief appearance in The Crow movie, where Eric shouted "Let her go" and Top Dollar responded by shrugging and saying "All right".
There's a heroic example in Hancock:

"You want down? I'm good at down! I'm really good at down!!!"

—Hancock, right before slamming some criminals' car into the Capitol Records Building.

In Pirates of the Caribbean: The Curse of the Black Pearl, Will demands of Barbossa that he release Elizabeth. However, he "failed to specify when or where" to quote Barbossa, resulting in her being forced to walk the plank. They were near a deserted island though, so she didn't drown.
In Analyze That, Paul Viti and his bodyguard, Jelly, are interrogating a snitch, which leads to this exchange after they get their information.

Paul: "Alright, pull him up."
Jelly drops him.
Paul: "What're you doin'? I said pull him up."
Jelly: "No, you said drop him."
Paul: "No... I said pull him up!"
Jelly: "I specifically heard you say drop him!"
Paul: "No, you heard what you wanted to hear."
Jelly: "... you got me there."

This happens near the end of Enchanted, while Robert attempts to protect Giselle from dragon-form Queen Narissa:

Robert: Over my dead body!
Narissa: ...OK. I'm flexible.

Freddy pulls this one in A Nightmare On Elm Street 3 Dream Warriors. When the heroes show up to save Joey, who's tied up over a fiery pit, Nancy (who, having fought Freddy before, should really know better) shouts "let him go, Krueger!" Of course, Freddy replies, with a sarcastic bow, "your wish is my command": Joey's sent plummeting into the pit, and is only narrowly saved by the rest of the group.
This happens in the Disney/Walden Media movie version of Prince Caspian. When some Telmarines are about to dump Trumpkin, bound and gagged, into the river, Susan shoots an arrow and orders them to "drop him". They do so - unsurprisingly, into the river, and the boys jump in to save the dwarf while Susan dispatches the soldiers. Trumpkin is suitably unimpressed, and treats Susan to a bit of snark once they're all back on dry land.
In a movie about the Dutch occupation of Indonesia, some soldiers have a prisoner tied upside down and are torturing him. An officer orders them to let the man go, so they cut the rope so he falls on his head and breaks his neck.
Semi-heroic example in Max Keeble's Big Move: when Max tells the nerds to "let the bullies go" after threatening to throw them in a dumpster, they comply... by dropping them in the dumpster.
In The Toxic Avenger, when Toxie confronts the hit-and-run driver Bozo in Bozo's car, the youngster tells Toxie to "give him the wheel" so he can drive straight. Well, Toxie dislocates the steering wheel and hands it over. Cue Oh Crap look on the driver's face - and a collision-induced explosion.
In Underworld Rise of the Lycans, Viktor seizes a dissenting(Human) silver mine owner by the throat. The man croaks "Let me go." Viktor complies, Hurling him headfirst into a massive stone pillar.

Literature

A variation in Artemis Fowl. When Briar Cudgeon is told to put Artemis down, he responses, "I'll put him down, alright."

Live-Action TV

Played for laughs in Chuck Versus The First Date:

Casey: Let the geek go!
Sarah: Wait! Not out the window!
Casey: Aren't we picky?

In one episode of Babylon 5, Delenn demands that the Streibs release their prisoners, and they do: into outer space.
- Which wasn't very smart as they had an already angry warship right on their heels that no longer had a reason to hold back and summarily destroyed them.
Played for humor on an episode of Get Smart. The Chief yells, "Drop that Control agent!" to some henchgirls holding Max out a window; Max later points out that his words could have multiple interpretations.
Happens in an episode of Psych.

Tabletop Games

Combined with Literal Genie, the GURPS manual has a spell to animate a machine or vehicle, but warns you it takes you commands literally. Saying "Drop me off there." to an animated helicopter is specifically mentioned.

Video Games

In Sam and Max: Culture Shock, Sam and Max get information out of Jimmy Two Teeth by holding him out the window. When Jimmy demands that Max put him down, Max, as befits his status as a Heroic Sociopath, drops him.
In Star Wars: Bounty Hunter, Jango Fett is holding a senator over the edge of the balcony of his penthouse apartment. A police ship appears and orders Jango to release the senator. Jango complies.
In Batman: Arkham Asylum, Batman confronts the Joker; they are separated by a pool of water. Joker's holding a guard hostage, and Batman orders Mistah J to let the guard go, which the Joker does. To be fair, he does so after he kicks a generator in the water and moves the guard over the water. If you sequence break by cutting power to the pool before heading to it, the guard's already dead.
In World of Warcraft, there is a quest where you are sent to take a cultist prisoner. He surrenders, then grabs you and tries to throw you off the flying ship. Luckily, your backup arrives, and dangles him over the edge, prompting him to yell

You! Let me go now! Wait...no! Don't let me go!

In Forever's End, the Black Demon is holding Hyuuga over a cliff edge, and Epoch tells it to let him go. Splat.

Web Comics

Taken to literal extremes in this Super Stupor strip: "Nothing unhands you like a garbage disposal."
Buck Godot makes this mistake here.
Riff from Sluggy Freelance demands this of the demon K'Z'K when it dangles Riff's mom off the edge of the Empire State Building. He immediately realizes "Drop my mom now!" probably wasn't the best choice of words.
Sidekick Girl is Genre Savvy enough to know not to say this, but Illumina isn't, as seen here.
The Dreamland Chronicles: The pirate laughs and observes Alex doesn't really want it.
Sam Starfall, from Freefall, does it to himself, here.

Web Original

In Darwin's Soldiers, Jayden tells Trinity to let Kiara go. Trinity obliges...and then drop-kicks Kiara into a tree.

Western Animation

The pilot of Darkwing Duck, with Gosalyn being held high in the air by the villain's vulture (or condor or something) to force Darkwing to give up the code for a weapon. Saved by Launchpad, who happened to be flying by when the bird let go.
- Or was actually following the events and reacted appropriately.
In Chip 'n Dale Rescue Rangers, "Adventures In Squirrelsitting", Fat Cat holds Tammy and Bink by their tails, and demands the Maltese Mouse in exchange. Said artifact is given up, followed by the demand, and the literal fulfillment. Monty catches Bink (with an assist from Dale), and Chip catches Tammy, setting her up to be the Clingy Jealous Girl for an episode.
The Powerpuff Girls: In one of the Time Travel episodes, the girls grab Mojo Jojo as he's falling into the town volcano. Mojo can be heard off-screen screaming, "Put me down! ... No, don't put me down!"
The Secret Saturdays: The Saturdays battle a monster in Japan that drops somebody like this.
In the Pinky and The Brain episode "Brain Noir," Brain is climbing out of the water and grabs the hand of someone reaching out to help him. Then he realizes that the person in question is his archnemesis Snowball and yells, "Get your hand off of me!" Snowball, not unexpectedly, complies.
Done in The Tick (animation) vs. Pineapple Pokopo when Arthur is captured by some Mooks. Of course, Arthur can fly, but he isn't particularly happy about The Tick's choice of words either way.
A less-fatal version of the "let me go" variation is used in The Prince of Egypt, in which Moses does this to Tzipporah, releasing the rope with which she's tied and allowing her to fall into a pool of water. She later returns the favor.
Heroic (of a sort) version in Robot Chicken. Ted Turner, having dressed himself as Captain Planet, forces someone to sign a pledge not to dump any more sludge by holding them out of a skyscraper window, after which he will let them go. The guy complies, and Turner releases him.
Self-inflicted version: In Batman Beyond: Return of the Joker, Ghoul captures Dana on a ledge in a several-story nightclub. While struggling with him, she tells him to let her go. He does, and she falls two stories onto a strobe light.
This happens at the end of the Veggie Tales episode "Sweetpea Beauty" when the mirror drops Sweetpea from the top of the castle. Prince Larry saves her, though.
Batman: The Brave And The Bold: In "Legends of the Dark Mite!", Catman is auctioning off a wild Sumatran tiger. Batman demands that Catman "Release him!". Catman obliges by opening the cage and letting the tiger loose on Batman.

Real Life

In 2010, Russian naval forces arrested a group of pirates that had taken over an oil tanker. However, due to what they saw as irregularities in international law, they had to release them. So they did - they were "released" into an inflatable boat, hundreds of miles from land and with no navigational equipment.
In 1952, police officers moved to arrest burglars Derek Bentley (age 19) and Christopher Craig (age 16) at a time when Craig had a revolver. Supposedly, after getting away from Detective Sergeant Frederick Fairfax, Bentley told Craig, "let him have it, Chris," which can be interpreted as an instruction to turn over the gun or an instruction to shoot. Fairfax was shot in the shoulder. Shortly thereafter, Police Constable Sidney Miles was sent onto the roof and fatally shot. Craig and Bentley were found guilty of murder, Bentley was executed, and the execution was so controversial that it arguably led to the abolition of capital punishment in the U.K. In 1998, Bentley's murder conviction was posthumously quashed.