Double Date

Couple Alice and Bob go on a double date with couple Carlos and Dana.

Character Alice and Carlos are actually far more interested in each other than their dates (see also: Star-Crossed Lovers). In fact Bob and/or Dana are often The Beard and usually wind up with each other by the end of the episode, providing An Aesop about being forthright and honest.

Often comes about because Alice and Carlos are trying to deny their attraction (see: Will They or Won't They? ), as an attempt to prove they're over each other when they're not, or to make one another jealous.

Anime & Manga

 * Happens early on Lovely Complex too.
 * In Ranma ½, Ranma goes on a date with Ukyo so he can spy on Akane's date with Ryoga. Ryoga and Ranma inevitably end up fighting, and both transformed into their curse forms.
 * At the start of Marmalade Boy, a play on this is the explanation behind the current relationships of the main characters' parents, though the truth is more complicated.

Film

 * The movie Keeping the Faith, although one of the couples on the double date are in fact the other character's best friends, only pretending to be on a date, and only there for moral support.
 * Bonus points for one of the best friends being a priest.
 * When Harry Met Sally... has a flagship use of this trope, including "Bob" and "Dana" getting together.

Live Action TV

 * Castle does this in "The Third Man"; though he and Beckett are more interested in talking about the case at hand than each other, it does end up the same: They step out to solve the case, and their dates hook up.
 * The Cheers episodes "Save the Last Dance For Me" and "Diane's Perfect Date".
 * Happens on Noah's Arc, with Dre (who is with Noah's ex Wade) inviting Noah over for dinner. Unbeknownst to Noah, this is to set him up with Dre's friend Quincy. Though theres clear Unresolved Sexual Tension between Wade and Noah, in later episodes Noah actually does start to fall for Quincy.

Theatre

 * Shakespeare's A Midsummer Night's Dream makes it one of the oldest in the book. It can be even seen even as a triple date (counting Titania+Oberon).

Web Comics

 * El Goonish Shive: Tedd and Grace with Ellen and Nanase. This led to Tedd and Ellen finally making progress in their friendship, though they may disagree on whether it's a preexisting friendship or a new one, due to Ellen being an Opposite Sex Clone of Tedd's best friend Elliot... it's complicated.
 * In Kevin and Kell, post-divorce Martha and George go through a period of taking dates to the same restaurant at the same time. At least once, this results in their dates leaving with each other while George and Martha sulk.

Western Animation

 * Kim Possible and Ron double dated with Shego and Mr. Barkin. Barkin and the kids felt awkward together, so the double date was a disaster.