Hot Coffee Minigame

A lot of video games involve characters. Sometimes those characters get it on. Of course, since this is a video game, it's only a couple more steps of logic to present those, err, activities as part of gameplay. The result is this trope, so named after the Unusual Euphemism used in Grand Theft Auto San Andreas. (See below for more details on its amusing history.)

Please note that this trope does not concern the depiction of sex in a video game; that falls under "Optional Sexual Encounter." This trope concerns when said encounter is interactive. If the player doesn't have some control over what happens, it doesn't count. This means games like The Sims are right out, since you can tell your characters to "Woohoo," but the act itself is a Cutscene with no interactivity. Of course, Rule 34 being what it is, there are Game Mods which make Woohoo interactive. Those do fall under this trope. (Again, more on that below.)

This trope often crosses over with Optional Sexual Encounter, since (most) games do not make sex mandatory. Often overlaps with IKEA Erotica ("press B to thrust!").

Action Game

 * Each God of War game has one. Amusingly, they are Safe For Work Everywhere But America (SFWEBUS), since the Quick Time Event takes place against a Sexy Discretion Shot background.
 * III seems to have missed the point of a Sexy Discretion Shot. When the minigame starts, the camera pans... to Aphrodite's two half-naked handmaidens fondling each other while watching the action and eventually starting a private minigame themselves offscreen.
 * Rule of Funny, maybe?
 * Up to Eleven in the Ghost of Sparta, where Kratos visits a brothel in Sparta and manage to entertain EIGHT women at once.... it must have been a really large bed!.

Adventure Game

 * The original version of Fahrenheit (2005 video game) has several sex scenes, the first of them being optional and interactive, which were both Dummied Out when the game was released in the United States under the title Indigo Prophecy. The developers claimed that the removal didn't affect the plot, thereby implying they were entirely gratuitous.
 * Not the plot, maybe, but certainly the characterization.
 * Heavy Rain also features an interactive sex scene.

H-Game

 * Many porn games have this, especially Hentai.
 * If the game is by Illusion, this probably is the game.

Platform Game

 * Parodied in Achievement Unlocked 2, where the elephant protagonist runs and leaps around a giant coffee mug.
 * Another Flash platformer, Humbugger, in which you play a chicken, has a sequence in which a rooster appears out of a bush. Chicken and rooster then disappear into the bush together, and the top of the screen becomes a reaction game. Hitting the right keys causes the bush to shake, and the game gets steadily faster. Completing this game causes an egg to roll out of the bush. A chick then hatches from the egg, and becomes the new playable character for a while.

Real Time Strategy

 * Star Control II has this within the storyline, though it's not especially smutty (the screen goes black and the Dialogue Tree goes suggestive).

Role Playing Game

 * Mass Effect gets an honorable mention here. It does not actually exhibit this trope, as its Optional Sexual Encounter was completely non-interactive, but it was accused of having such a minigame (incorrectly) at the height of the Hot Coffee scandal, and reaped the rewards of free press.
 * Special mention goes to Jack Thompson, who, for some reason, believed the "scandal" was overblown. This is coming from the same guy who called Grand Theft Auto and every other First-Person Shooter a Murder Simulator.
 * Temple of Elemental Evil, a Dungeons and Dragons video game made by Troika, originally had a brothel that was later Dummied Out. With the Circle of Eight Mod Pack, it becomes available again. Inside, the player can purchase sexual favors in dialogue which "leave very little to the imagination."
 * Final Fantasy X-2: comes damn near this trope; there's a minigame about halfway through where Yuna disguises herself as an enemy goon, goes to her arch-rival's mansion, and winds up unwittingly drafted into a massage minigame. Said rival tends to let out an orgasmic "AH! THERE!" when you hit a sweet spot;" there's also some snarky innuendo before and after from her two chief goons.
 * For those that remember, Incredible Crisis had a similar minigame in a ferris wheel. You'd know you done good when she started moaning... and the wheel started lighting up the more it went on.
 * At least two different mods add such minigames to The Elder Scrolls IV: Oblivion. One is actually pretty decent, if you can find the translation patch and get past the Nintendo Hard-ness of it.
 * There also exists a rather well-done and popular mod of that kind for its predecessor, The Elder Scrolls III: Morrowind.
 * The Neverwinter Nights mod A Dance With Rogues took the easy route and used the dialogue system to create some.

Simulation Game

 * There's a few dating sim games on Newgrounds that have this, usually in the form of 'alternate pressing up and down' or just plain Button Mashing.
 * As mentioned, The Sims does not support this out of the box, but people have changed that with Game Mods.
 * Plenty of that in 7 Sins, where sex is definitely not optional. During the scenes (where both parties leave their undergarments on), the player has to finish one or several Mini Games with the sex as the backdrop. Successful completion of the minigame results in the character's increased affection for you, while a failure is not seen favorably. The sounds made by the player's partner during the minigame reflect how close he is to completion.
 * Custer's Revenge; the first rape simulation game? Or H-game?

Stealth Based Game

 * Borderline example with Assassin's Creed II. One of Ezio's conquests early in the game involves Action Commands to kiss the girl and take her clothes off.

Turn-Based Strategy

 * Amiga-era game Defender Of Rome had an example, if you managed to negotiate a peaceful alliance with Egypt. Cut to a night encounter with Cleopatra, where you have to negotiate a different kind of alliance...

Wide Open Sandbox

 * The Trope Namer is Grand Theft Auto San Andreas, a game which, as released, does not actually let you control the player's sexual activities. This function was programmed in, but later isolated from gameplay so that there was no way to reach it; hackers discovered it, prompting a huge furor from Moral Guardians. Rockstar Games benefited from the press but lost a lot of money from the lawsuits, as well as from having to pull the game from shelves to be fixed and re-released.
 * With Grand Theft Auto IV, the reactions of the Moral Guardians are Hilarious in Hindsight. While you still do not see anything when you go up to a girlfriend's apartment, the prostitution cutscenes have gotten upgraded to a full Optional Sexual Encounter - including a choice of services, and realistic animations to go with them. While the characters remain clothed, it essentially boils down to Hot Coffee - minus the interactivity. While that itself means that it isn't part of this trope, it's still pretty interesting that the Moral Guardians haven't said 'boo' about it. Apparently sex is okay in video games, as long as you can't interact with it.
 * Also, appreciate the Irony: despite all the various illegal activities one can do and the Video Game Cruelty Potential that exists in the series, a perfectly legal and consensual heterosexual encounter is what raised the most controversy.
 * Saints Row 2 has a button-matching minigame when the PC has sex with random people in secluded locations.
 * And you didn't even get to see anything. Waste of a perfectly good Virtual Paper Doll.