Well, This Is Not That Trope

"Greenslade: Into this complex world of crime, of move and counter move, stepped a man of great ingenuity, daring, resource and brains.

Eccles: Ain't me, folks."

- The Goon Show

You know how when someone describes something they actually tell you about the thing itself? Well, This Is Not That Trope.

Subversion distilled to its purest essence: you directly build up the audience's expectations with an elaborate description of something, then tell them that you're actually talking about something else.

Most often a Comedy Trope, but can be Played for Drama if done correctly. Compare Dissimile, Analogy Backfire, Bait and Switch Comparison. Related to Bait and Switch Credits.

Examples:

Comic Books

 * Watchmen: "You know the kind of cancer you ultimately get better from? ...That ain't the kind I got."

Fan Fiction
"The walk back was uneventful.
 * From chapter 8 of Rob Haynie's Ranma One Half fic, Girl Days:

No, sorry, that was a different walk back. THIS walk back was something other than uneventful."

Film
"Narrator: I'm sorry to say that this is not the movie you will be watching."
 * A Series of Unfortunate Events opens with in Sugar Bowl (not that one) with a sickenly sweet musical number and an adorable dancing elf. It's cut off by the narrator.

"Helen: "Remember the bad guys, on those shows you used to watch on Saturday mornings? Well, these guys are not like those guys. They won't exercise restraint because you're children. They. Will. Kill you if they get the chance. Do NOT give them that chance.""
 * The Incredibles uses this trope seriously:


 * One of the trailers for the 2011 Muppets movie sets it up to look like a generic Rom Com -- until the Muppets show up halfway through. The characters look as surprised as we are.
 * Bookended with the final trailer, which inverts the previous joke by advertising the Muppet movie... then having the Muppets be surprised that there are humans in the movie too.
 * The trailer for Monty Python and The Holy Grail starts by talking about how there are some movies that change the film industry forever, like The Seven Samurai and Ivan the Terrible. Then it mentions that there are also more run of the mill movies, like Herbie Rides Again and Monty Python and The Holy Grail. After going on about how the movie is rather silly instead of serious fare, it then segues into a commercial for a Chinese restaurant for no particular reason.

Literature
""And then, one Thursday, nearly two thousand years after one man had been nailed to a tree for saying how great it would be to be nice to people for a change, a girl sitting on her own in a cafe in Rickmansworth suddenly realized what it was that had been going wrong all this time, and she finally knew how the world could be made a good and happy place...
 * Done twice in Piers Anthony's book Under A Velvet Cloak. First he describes the story of King Arthur and follows it up with "This is not that story." Then he describes the story of a girl who would be an ancestor to many Incarnations and says "This is not that story either."
 * The Hitchhiker's Guide to the Galaxy:

This is not her story.""

""Scaling Everest was, by far, the most amazing and transformative experience of my life. Unfortunately, this is a thesis on context-free grammars.""
 * Even this subversion is subverted a few books later, in So Long and Thanks For All The Fish. It opens up the same way as Hitchhiker's Guide, then says, "This is her story."
 * There's also a sequence where Arthur asks Ford about how the universe was born, and Ford goes off on a tangent about buying a bathtub, filling it with sand, then watching all the sand drain down while filming it, and then playing the film back in reverse. Which, he adds, is nothing like how the universe was born.
 * "Maybe once in a lifetime, there comes a book with such extraordinary characters, thrilling plot twists, and uncanny insight, that it comes to embody its time. Atlanta Nights is a book." — Adam-Troy Castro
 * The winner of the 2007 Lyttle Lytton Contest freeform challenge:


 * The Adventures of Pinocchio opens with one: Once upon a time, there was a king! No, there was a piece of wood.

Live Action TV
"Know that famous Street where all the sunshiney happy kids go to watch quality TV and learn stuff? THIS AIN’T IT!!!"
 * On Malcolm in the Middle, Lois tells Reese, "Some people have book smarts; some people have street smarts. You have neither."
 * One of the sketches on Monty Python's Flying Circus featured a narrator who would introduce various on-screen characters in detail, only to remark that they were not going to be the protagonist and move on to someone else they run into. This happens several times.
 * Subversion: The "Science Fiction Sketch" begins by introducing Mr and Mrs Brainsample as a "perfectly ordinary couple" and promptly disregards them as being too ordinary to be of interest. Then they reappear at the sketch's climax...
 * In the Wonder Showzen Season 1 DVD, we have this:

"Prue: Have you ever seen that television show where there's the woman who's an angel and she helps strangers every week?
 * In the Charmed episode "The Wedding from Hell":

Allison Michaels: I love that show.

Prue: Don't get too excited, I'm nothing like that."


 * On Roseanne: "Mark, remember all those times you screwed up? This aint one of them!"

Radio
""For a show such as this to have lasted thirty years might be thought achievement enough in itself. But to have brought joy and laughter to thousands of listeners ... might at least have been worth a try.""
 * Often done with the introductions on I'm Sorry I Haven't a Clue. "People come to this theatre from far and wide to watch the greatest performers of the age. Other times, they come to see our teams..."
 * Celebrating the 30th Anniversary Special:

Western Animation

 * Computer Animation Showcase, a collection of computer-animated shorts, started one of them with this voiceover: "Every once in a great while, a movie comes along that touches everyone's lives. *beat* Eh, but not this one.
 * In one Animaniacs episode, the Warner siblings are being chased off. Soon enough, they start climbing back into the water tower, and Yakko sobs, "I know when we're not wanted." When the antagonist is gone, he adds, "And now is not that time," and climbs back down.
 * Only one hero can track down Cave Guy. Only one hero has the heart to fight this fiend. That hero is... On another network. Thus we have no choice but to turn to this fellow.