In Revenge of the Nerds II: Nerds in Paradise they advertise their party by altering the neon sign of "Hotel Coral Essex" to read "Hot oral sex".
In The Beach Girls a no holds barred sex, drugs and alcohol orgy is followed by a pot party/sex orgy at Uncle Carl's house at Paradise Beach over Memorial Day weekend.
In Rock Star the after party following a Steel Dragon concert really does turn into an orgy. The film features an amusing "morning after" scene where the protagonist rolls out of bed, leaves the bedroom, and finds literally dozens of naked people passed out on the floor of his hotel suite.
Velvet Goldmine - innocent new wardrobe mistress Shannon is led by Jerry De Vine into a distinctly uninhibited party of stars and crew, all laying about on floor cushions.
Animal House references the trope. After the fraternity decides to have a toga party, one of the brothers is shown vehemently explaining to his girlfriend, "It's not going to be an orgy!"
The Friendsy's scene in Seeking a Friend for the End of the World turns out to be this. In the short time before the world is destroyed, the restaurant decides to party it up and be as friendly as possible with the customers and each other, and often a bit too friendly.
A Hard Day's Night - The Beatles, confined to their hotel suite, discover Paul's grandfather has borrowed an old waiter's formal clothes and gone out to a gambling club. Paul, anxious about it, concludes "He's probably in the middle of some orgy by now!" They all react with excitement at the idea and rush out to find him.
Old Waiter: Wait, what about me?
John: You're too old.
Superbad has the two main characters inadvertently get tangled up in one of these as they head to the party they are supposed to attend. It doesn't go very well for either of them.
In Smokin' Aces, Buddy Israel's penthouse apartment is obviously showing signs that the party held the night before the action of the movie starts was one of these. Naked women abound, furniture is knocked over, and Buddy gets really, really pissed off that someone somehow got "human ejaculate" if you know what I mean and I think you do on his best suede jacket.
In Stephen King's The Stand, Larry Underwood throws a party at a beach house after hitting the big time with his single, "Baby Can You Dig Your Man." This party goes on for a few days, and the narration mentions that something that sounds like an orgy is happening in the basement.
In Kushiel's Dart, Melisande hires an entire brothel (a high-class establishment practicing one of the most honoured professions in that particular culture, but still a brothel) as the setting for her lover Prince Baudoin's birthday party. Longest Night parties, for courtesans, are similar.
in Michael Swanwick's Bones Of The Earth, a party among a group of researchers turns into this, thanks to alcohol and triceratops mating displays. Long story.
In the chronologically first novel, Driz'zt and some other recruits at the academy are ordered to participate in the initiation rite of new young priestesses. Having completely different morals than the rest of drow society, he is seriously freaked out when he realizes what kind of ceremony it is and for what kind of "assistance" the male recruits were needed.
Jerry Cornelius stages a party like this in The Final Programme, and breaks up a party (with machine guns) that's got bits of this going on in The English Assassin.
The first episode of Skins is about Sid trying to lose his virginity at a party, and pretty much every party in that series features rampant drug use and sex.
In City of Men, 'funk dances' are a prime location for making out and hooking up.
Crews and Reese crash one of these in the Life episode "Dig a Hole," hosted by two computer-nerds-made-rich.
Inverted on Degrassi The Next Generation: A party actually interferes with Emma and Sean having sex. Especially when one of the guests dies.
Spoofed in the German sketch-comedy Switch Reloaded, which had a skit where there was a commercial for a broom with spikes at the end for poking such guests in the heels to bring them to leave.
True Blood had Maryann parties; parties also known as incredible orgies in the middle of the forest. Incredible orgies used as a tribute to Dionysus that turn humans crazy
Since Jesse can't stand being alone for more than a few hours, there's one going on at his house throughout the first half of the fourth season of Breaking Bad.
In a second season episode of Party Down, the company is unknowingly hired to cater a party that is meant to be one of these. The invitation was so badly worded that none of the guests realized it, either.
In one season one episode of Sliders, the gang slide into a world about to be struck by a species killing asteroid, that never developed nuclear weapons and has no way to stop it. During their time there, they come across a group of revellers who've decided to have a nonstop party 'til the world ends, including lots of getting extremely liquored-up, sex with anyone who comes near you, and even a game of Russian Roulette in full swing. Then Quinn and Arturo develop the world's first nuclear warhead, it gets shot up on a cruise missile and destroys the asteroid, and the people of the world are extremely embarrassed as a result.
Inevitably riffed on in MST3k; during a screening of Laserblast. The protagonist is at a birthday party looking through the house for his girlfriend. To be fair to the trope, he has already wandered past one couple who were making out. He opens a door and pokes his head in:
Tom Servo: Hey, there's a dozen naked teenage girls in there! That's what happens at these teen parties - it's true!
Really, there's too many music videos to list.
Bob Seger's "Horizontal Bop" tells about someone trying to get one of these started:
Somebody bring the records Somebody bring the brew Someone get a house Buddy, we'll know what to do Someone tell the ladies Someone make a deal If we can't find a house Then someone find a field Grass is good as carpet Anyplace is fine It's time to get rockin' Babe it's time to shine Tell 'em we'll be dancin' Dancin' til we drop It's time to get down and do the horizontal bop
The parties of the Val'Sullisin'rune clan in Drowtales often turn into this. But given the cultural sensibilities of the Drow this isn't seen as a negative, and the parties are generally a fun time for all.
Inverted in Moon over June, when a prior hookup bumps into Summer and invites her to a "group thing" she is part of that is getting together for a session that night. Cue Sex Addicts Anonymous meeting.
Being Moon over June, it turns into exactly this kind of party anyway.
In Futurama, Hedonism-bot has a party that is basically an orgy, except then almost everyone there gets blown up.
Hedonism-bot: Everywhere I looked, there were piles of bodies... and then the explosion struck! Ah ha ha ha! Oh hoo hoo...
An example from Regular Show (hey, it is meant for teens...kinda):
Benson: It's almost 8 o'clock. Kill the lights!
Muscle Man: (unzipping noises) Woohoo! Skips is going to be totally surprised when he walks in and sees us totally naked!
Benson: ...it's not that kind of party, Muscle Man.