NOT!

"''"Of course, the Sue, being noble enough to attract the attentions of two high-ranking Elves, said that she would be betraying Legolas’ trust if they slept together, and it would constitute a marriage according to the customs of the Eldar, and therefore it was best to refrain. Not.""

- Protectors of the Plot Continuum, Your Unhappy Elladan

Popular expression during the late 1980s and well into the 1990s, where someone would describe an event happening by stating the exact opposite then saying in a louder tone of voice, NOT!

For example, describing the database hack this wiki experienced in 2015 that temporarily wiped out the whole website, it could be said that, "We really enjoyed it and had a marvelous time getting the wiki back online. NOT!"

This usage of saying something then saying "NOT!" at the end, actually goes all the way back to the 19th century (when "...I don't think!" was a variant), it just became cool again back during the 1980s.

In traditional English, this is known as Sarcasm.

Popularized by the movie Wayne's World. (along with That's What She Said! and other Totally Radical Stock Phrases of The Nineties).

The evil version involves the phrase I Lied.

Anime And Manga
"Ranma: Gee, I never realized how cute you were before. Shampoo: Then you love Shampoo? Oh! So happy! Now, we live happily ever after- Ranma: *grabs the pork buns* Ha! Not!"
 * Ranma pulls one of these on Shampoo in Ranma ½ after he snatches the pork buns she made that could force you to follow a command after a certain signal is given:

"Shampoo: Is mine, now! Ranma: *takes it back* Not!"
 * Also said in the manga when Shampoo takes from Akane what she thinks is an engagement ring from Ranma.

Comics

 * In the first Death mini-series, Sexton mocks a guy for saying it.

Film
"Preacher asks the "do you take this man?" part. Kate (gathers herself): I...will...n-- Petruchio kisses her, so she doesn't manage to get out that last word. And so they're married! Hooray!"
 * Borat had the titular character take a lesson on humor. His attempt to understand the concept of "NOT!" became a Running Gag throughout the movie, with him finally getting it in the end.
 * Do be careful with the usage of this. Kate from The Taming of the Shrew tried to get out of a marriage ceremony thusly:

Literature
""Heavens, yes! What modern girl could live like those inane females?" "They were the models for our mothers." Marjorie laughed. "Yes, they were--not! Besides, our mothers were all very well in their way, but they know very little about their daughters' problems.""
 * Dave Barry suggests in Dave Barry Does Japan that, since Japanese people are obviously humor impaired, they should begin adapting American jokes that are most easily adapted to foreign cultures. He starts with "NOT!"
 * Used in this passage from "Bernice Bobs Her Hair", written by F. Scott Fitzgerald in 1920:

Live Action TV
"Master: "Why don't we stop and have a nice little chat while I tell you all my plans and you can work out a way to stop me, I don't think!""
 * The 1980s resurgence in use may have started with an MTV promo spot featuring Jim Turner of Duck's Breath Mystery Theatre, in which Turner plays both burnt-out hippy rock star Randee of the Redwoods and his business-suited alter ego, staring at each other through a mirror. After a brief, hostile exchange, his uptight counterpart departs and the image of Randee turns the camera to declare, "I like that guy...NOT!" To the best of his recollection this was the earliest (recent) instance of this usage that this troper encountered.
 * Wayne and Garth in SNL Wayne's World skits.
 * Featured in The Movie, of course, and not invoked by only Wayne and Garth. After spending time with the two, Benjamin's dragon Russell catches himself doing it, expressing regret immediately afterwards.
 * Doctor Who, during the Master's triumphant return with more Genre Savvy:

"Mr. Stein: You may think that just because I've been in London all this time that I've failed to notice this office's deficiencies. Well...I have. (beat) NOT!!"
 * Robin Hood has another variation with one of the Sheriff's many Catch Phrases. "A clue: No."
 * Michael uses "It's been fun...not," on Arrested Development. The narrator comments that he wishes he could have come up with something cleverer, or at least less dated.
 * If The Soup catches you doing this, they'll call you out on it.
 * On Will and Grace, Will's long-absent and eccentric boss, Mr. Stein, turns up unexpectedly in the office:


 * In an episode of Psych, Shawn tries to bring "not" back. He then decides to also revive "said the liar" only to have it pointed out that the two cancel each other out if used at the same time.
 * A scene from The Office which cannot be described, but must be seen: Enjoy!

Music
"I could walk out now, get in my truck Never look back, forget your love Sure, I could leave, 'cause I'm tough enough...Not!""
 * "Not", a song released by The Bellamy Brothers in 1993, is this trope in song:

"Weird Al: I really LOOOVVVEE you...NOT!"
 * Used in the "Weird Al" Yankovic song I Was Only Kidding


 * Al has stated that he actually removed a song from Off The Deep End so that he could use this one before the joke got old and obnoxious.
 * Steven Curtis Chapman's album The Great Adventure has an intentionally corny rap song called "Got to B Tru", in which Christian rapper Toby MacKeehan makes the following observation about SCC's rap skills at the end of the song: "I think rap music is most definitely you!" *record scratch* "NOT!"

Video Games
""I suppose I misjudged!" Casts Haste on self "Fighting all four of you..." Casts Protect on self "...is just too tough for me..." Casts Shell on self "NOT! Ha, I lied! Like a rug! Oh, I kill myself!" Attacks heroes"
 * Gilgamesh crosses this with fake surrender in Final Fantasy V after getting badly beaten:


 * In Final Fantasy VIII, party can find and read magazines called Timber Maniacs. When trying to read the  one found in Zell's house in Balamb, the message reads: "An old issue of [Timber Maniacs]...............NOT!"

Western Animation
"Sentinel: Surrender, Mutant. Cyclops: Of course... NOT!"
 * Iago in Aladdin uses it to describe the sultan. "Oh, excellent judge [of character], sure... NOT!"
 * Sarah on Liberty's Kids used the "I don't think" version often.
 * X Men the Animated Series episode 'Night of the Sentinels Part 2' has this trope with Cyclops as he is about to take down a sentinel.

"Matau: "Look, everybody! It's Keeetonguuu!" * beat* Matau: Not."
 * Bionicle: Web of Shadows:

"Poochie (voiced by Homer): "Catch ya on the flipside, dudemeisters...NOT!""
 * In The Simpsons episode "The Itchy & Scratchy & Poochie Show":

"Jade: Excuse me... not!"
 * Jackie Chan Adventures season 5, episode 1:

Other Languages
"Parent to kid: "You have to learn how to deal with money, so I will raise your pocket money... NOT!""
 * In the German Language, due to more liberal word order, normal sentences can end with "nicht" (not), which may remind English-speakers of this trope. Example:


 * This concept translates directly into Japanese. In anime and manga, it's fairly common for a sarcastic character to start explaining something and end it with "-ja nai!" ("...is not!") with the same meaning as the sarcastic "NOT!"
 * A variant is to end a thought with "...is what I'd like to say," meaning that while they'd like to say all that, the truth is the opposite. This is generally used when the intent is a softer let-down than the abrupt brush-off of "NOT!", assuring the person that they're not being put off lightly or given a mere excuse. But it does sometimes get used to be just as cruel as the ruder variant, depending on the context.