Mother-Daughter Threesome

I have an idea; you both take your clothes off, and I'll close my eyes and try to figure out which one's the mother and which one's the daughter!

—Ken Titus, Titus

A common male fantasy involves scoring with a hot girl and her equally Hot Mom—at the same time!

As with many Porn Tropes, this is probably better as a fantasy than a reality. And guys, we really don't recommend ever telling your significant other that you'd like to involve her mother in your sex life. And suggesting that you'd like to involve her daughter might be even worse. (And if she says yes you might want to consider running very far away.)

Oddly enough, the reverse situation—a woman scoring with a hot father and son pair at the same time—almost never occurs.

Sometimes subverted when the hero gets together with a more mature lady who asks if he's up for some mother/daughter action, and while he thinks she means her and her daughter, Hilarity Ensues when it's revealed that she meant her and her mother.

Examples of Mother-Daughter Threesome include:

Anime and Manga

The Hentai OVA Anyone You Can Do...I Can Do Better has this towards the end. Or So I Heard.
In the Hentai manga Super Taboo, the protagonist Yuu has a drunken threesome with a mother and daughter who also happen to be his mother and sister.
The Hentai Boys Empire decides to take it a step further by throwing in the guy's mother as well—in fact she's the one that started it.
Basically, any Hentai with a male protagonist and a mother and daughter would invoke this trope.

Comic Books

In Ironwood, an erotic comic by Bill Willingham, Bishop-Major Simon Passover has sex with a mother and daughter, and then kills the outraged husband/father in a duel when he arrives home.
In the Cherry comics, Cherry Poptart and her mother Pepper often end up having sex with the same guy (before having sex with each other).
Lesbian threesomes involving a mother and daughter pairing are not unknown in the Housewives At Play comic book, much in the same way that a bit of heat is not unknown on the surface of the sun.

Film

In Machete, the eponymous character scores with June and April Booth in a three person pool party.
In End of Days The Devil does this with the family of his minion, whom he killed. Then he does some weird absorby thing to them.
Averted in The Graduate. Ben never actually sleeps with Elaine during the course of his affair with Mrs. Robinson. One presumes that they do later, but that's another story.
In Almost An Angel, Terry Dean is implied to have had a fling with a woman and her daughter in a hot tub.

Literature

In Charlaine Harris' novel Dead Until Dark. Liam, a vampire, has sex with (and takes blood from) a mother and daughter. He glamors them, but does not erase their memories of the encounter.
The Victorian pornographic novel My Lustful Adventures: A Nocturnal Meeting is this: the hero rescues a mother and daughter (aged about forty and nineteen) from ruffians and is taken into their home. Hijinks ensue from there, the main action providing a framing story in which the female characters' backstories are expanded on. The women take a very co-operative lead in seducing him, and pretty much anything goes (including mother-daughter incest).

Live Action TV

A Cheers episode had Sam daydreaming about this—the teen-aged daughter of one of his girlfriends (who called him "Uncle Sammie") started talking to him about male-female attraction. It turns out she was actually talking about her new boyfriend. IIRC, the commercials made much more of it than the actual show.
In the Nip Tuck episode "Cindy Plumb", Dr Christian Troy has a mother/daughter threesome with nurse Riley and her mother Jill White. When he asks the daughter if they do this often together, she reveals that the first time was when her mother walked in on her making out with her stepfather. He throws them out of his apartment not long after that because "this is too screwed up even for me".
- On another occasion another women offers the same by essentially trying to pimp out her 17-year-old daughter along with herself in exchange for plastic surgery. Suitably disgusted, Christian declines and walks away.
Dylan apparently has a dream about this involving Claire and Haley in the Modern Family episode "Chirp".
In the episode "High" of Rescue Me, Mike is at a bar, and a hot cougar asks him if he's up for a little mother-daughter action. But then he finds out that she's the daughter...

Music

Taken Up to Eleven and Played for Laughs by Les Luthiers:

Mastropiero was an intimate friend of the Duchess of Lowbridge, mature woman whose charms had not diminished with the years... they had disappeared completely. Mastropiero feigned a fiery passion for the Duchess, but behind her back he was seducing her daughter, Genevieve. Thus he could enter the castle freely... to meet her granddaughter, Mathilde. This game of gallant pretenses gave excellent results. It was not the first time this system was used... by the three women.

Video Games

In Hitomi, Yoko forces Hitomi into a threesome with her and Yuki if Hitomi catches the pair of them on the couch.
Shippo mode in RapeLay allows you to play this straight.
Scarface: The World Is Yours. Have Tony talk to one of the pimps. Sooner or later the topic arises. It's called "Chicken and the egg" in street slang.
In Leisure Suit Larry 7: Love for Sail! Larry seduces mother-daughter country duet Juggs.
In Summer Days, Makoto can get one of these with Sekai and her mother.

Web Comics

Fansadox is very fond of this, including Birthday Gift and Confiscated Twins (in that case, it's a threesome only with the family members).

Real Life

The original Casanova reports being involved in one of these. For extra Squick, the girl involved was also his daughter.
- It's the game the whole family can play!
This is one of the various oddly specific things prohibited in The Bible.
Samuel Pepys mentioned in his diary that he participated in one of these, possibly at a larger orgy.