Koizumi from Haruhi Suzumiya uttered this at least on one occasion. The thing is, he did it just after one of his countless philosophical monologues. Just as he actually made Kyon feel uneasy about it, he responds "Just kidding, that's not what I think at all."
He also inverts the trope at one point, when suggesting that they deal with Haruhi's latest Reality Warp by convincing her that "It was all just a dream. *long pause* I wasn't joking, that was my idea."
England: God, [American Independence Day] is the worst day ever. I can't sleep for a week whenever it comes around; I just remember things. I feel sick, I feel terrible in the morning, I have nightmares, I can't eat, I can't work (and so on). Good that it's the end of this shit. I figured I might as well join a party or two at the end of this torturous week.
America: Me too, England. Whenever today comes around, I think of your white-eyed chagrined face. And how much of a poor loser you were. And I always feel awesome a week in advance.
This is November 11's Catch Phrase in Darker Than Black. His sense of humor is rather... Dark, shall we say, to which the deadpan addition of this sentence usually doesn't help much.
Mooks: ...And what do you plan to do with this 'acquisition', Mr. Smith? November 11: * Completely deadpan* Well to start I thought I'd walk through the doors of a rival company and kill 3000 of their best men. Mooks: ... November 11: ...Kidding.
Also an example from Mao which has the benefit of actually being funny. At the end of the episode with the body-stealing Contractor, he's talking to Hei about the benefits of the cat body he's trapped in. He asserts that he likes being a cat "because of all of the delicious kibble he's able to eat". After Hei gives him a look, he tells him he was joking and winks at the viewer.
There's some other very good ones too, like the one where November 11 might actually have been telling the truth:
Kirihara: So, is this your first time in town? November 11: No, I've been here for a couple of assassinations. Everyone else: ... November 11: Just kidding.
He also tends to be the victim of the occasional Ironic Echo, and Kirihara came up with the most fitting memorial to him possible after his death.
One, when Soichiro says that he might have a problem with Kira cleaning up crime and Matsuda reacts to this in surprise. The former comments he's just joking.
Two, Light joked about wanting to have Shinigami Wings, instead of their eyes.
Three is when Hatori attempts to leave Yotsuba. This doesn't spare him, though.
In To Love-Ru, Yui ends up in a compromising position with Rito while wearing nothing but a dress shirt (it's a long story). As she's been secretly crushing on him for quite a while and thinks that he's trying to seduce her, she heavily implies that she'd be willing to have sex with him. When Rito, being something of a Celibate Hero by-way-of Chivalrous Pervert, backs off, she claims that her offer wasn't supposed to be serious.
In the "Possession" arc of New Avengers v.2, Doctor Strange has been trying to protect the Eye of Agamotto from various supernatural attempts to take it from him, while trying to figure out who is behind it all. Spider-Man suggests maybe "Agamotto" wants his eye back. Cue the reaction panel, while Spidey asks "You mean there really is an Agamotto.. and that really is his eye?"
When a complete stranger seems to recognize him in Kyon Big Damn Hero, Kyon jokes to Haruhi that she might be a Slider that recognizes alternate versions of them from other worlds. Before he could say the trope name, Haruhi ran off after her. Kyon was right.
Films — Animated
In Madagascar, Skipper does this almost deliberately with Gloria.
Gloria: Where are the people?
Skipper: We killed 'em and ate their livers.
(Gloria stares at him in horror)
Skipper:(grinning hugely) Gotcha, didn't I?
Wreck-It Ralph: Sugar Rush is reset after Vanellope crosses the finish line, returning her to her proper place—princess of the game. Her first command is to have all the other racers who were mean to her executed. She did this merely to make them soil themselves in horror.
Vanellope: Stop cryin', Taffyta! I was just kidding!
Films — Live-Action
Forrest Gump: Not actually said, but it was strongly implied that LBJ's "desire" to see the wound on Gump's behind was actually intended to be a joke. Forrest, being Forrest, interprets this literally, and proceeds to oblige his "request" on live TV, causing Johnson to chuckle to himself and say "Goddamn, son!"
Hudson Hawk: Darwin Mayflower gives a pair of mooks a You Have Failed Me speech that ends with "We'll just have to kill you." His wife Minerva promptly shoots both of them, causing Darwin to protest, "God, Minerva, I was only joking!" Since they're the villains, though, he's not particularly upset about it.
Race for the Yankee Zephyr (1981). Theo Brown (George Peppard) has just threatened that something nasty will happen to Gilbert Carson (Donald Pleasence) if he doesn't lead him directly to the Yankee Zephyr, a crashed WW2 airplane holding a fortune in gold.
Gilbert Carson: Well it's a bit tricky. You see, the first time I saw the Yankee Zephyr, I was suspended arse-over-elbow underneath a Mixmaster. Theo Brown: That can be arranged. (Cut to Gilbert Carson tied up in a deer net beneath the villain's helicopter)
Selena: The beginning of the romance between Selena and Chris occurs when she asks him if he can dance and he says "Yeah, I put on my white shoes and black jacket and dance like John Travolta." She takes it seriously, prompting him to say he was just kidding.
Dumbledore:(sarcastically) If she means so much to you, surely Lord Voldemort will spare her? Could you not ask for mercy for the mother, in exchange for the son?
Snape: I have Ė I have asked him...
Dumbledore: You disgust me.
In the non-fiction book Homicide: A Year On the Killing Streets by journalist David Simon, one of the detectives receives a phone call from a police officer reporting another body and asking what they want done with it.
Detective: "We're a bit busy right now, so just throw it in the trunk of your car and bring it down to the homicide office."
Uniformed cop: "OK." ''(cop hangs up).
Detective:(frantically searching for the division's phone number) "Oh shit, he believed me..."
In the third book of the A Song of Ice and Fire, Roose Bolton finally decides to free Jaime Lannister after showing him a thoroughly unpleasant time at Harrenhall. On his way out the door, he tells Jaime to give Tywin Lannister his regards, and Jaime snaps back that Roose should be sure to give his own regards to Robb Stark. He's clearly just being sarcastic, but Roose actually does it. Although saying "Jaime Lannister sends his regards" while putting a sword through Robb probably wasn't what Jaime had in mind...
"Doppelgangland": Willow enters the library, where Giles, Buffy, and Xander are trying to come to terms with the fact that she's dead, because Xander and Buffy have seen her vampire counterpart from an alternate dimension:
Willow: What's going on?
Willow: (lightly) Geez, who died?
Willow: (panicked) Oh, God, who died?
Also when Xander and Buffy are about to get into a fight in "Dead Man's Party".
Oz: Okay, I'm stepping in, Mr. Referee Guy.
Willow: No, let them go. Talking this out isn't working, so let's try violence. [zombies burst through the window] I was being sarcastic!
In Supernatural, when the Winchester's lead suspect is an old woman who apparently had a stroke:
Dean: She could be faking.
Sam: What do you want to do? Poke an old lady with a stick?
Dean: (considers it)
Sam: You are NOT poking her with a stick.
There's an episode of Friends in which Rachel starts smoking in order to get in the important conversations her boss and coworker have in the smokers' room. The first time she lights a cigarette the following transpires:
Boss: I thought you didn't smoke
Rachel: Oh no, I thought you meant marijuana, I do smoke regular ones
Boss: We like drugs
Rachel: Me too
Boss: I'm kidding
Rachel: Me too
Subverted in an episode where Joey tries to come up with a new stage name. Chandler sarcastically suggests "Stalin" in response to "Joe." Joey, not knowing his history, takes him seriously. Subverted in that, while Chandler has this reaction visually, he then encourages Joey to actually use the name. His next audition does not go well.
Barbara Spencer: Blow an opening. With what? Don't tell me you know how to make a bomb out of a stick of chewing gum?
MacGyver: Why, you got some?
Played kind of horribly on The Big C when Cathy finally tells Sean about her cancer and Sean breaks down entirely. In a panic, Cathy blurts out that she was kidding, getting revenge on him for an early scene where he'd made her believe their father had molested him.
On Band of Brothers, Martin and Perconte have this exchange in the first episode:
Perconte:(showing off his polished boots) Now, just think, if you had any class or style like me, somebody might've mistaken you for somebody.
Martin:(show insignia on his uniform) Oh, yeah, like your fucking sergeant?
Taylor: The Dooses have been the backbone of Stars Hollow High hockey for years. I, myself, was the goalkeeper for our team in the last regional finals.
Lorelai: I did not know that.
Taylor: Oh yes. I was responsible for the game-winning goal.
Luke: So the puck just ricocheted off your head and into the net?
Taylor: Still counted.
Luke: For Godís sake, I was making a joke. You really got pucked in the head?
Taylor: No, I was making a joke, too.
A moment later Luke looks and claims that he can see the dent.
In Smart Guy, when Marcus learns that the "girl" he asked out were actually twins, TJ jokingly suggests that Marcus create a twin brother to get himself out of the situation. Unfortunately, Marcus seemed to take it as an actual idea suggestion from TJ and decides to ask them out, with TJ, horrified, then attempting to tell him that he was just kidding.
One episode of Leverage has Sophie interrogating an agricultural conglomerate's janitor under the false pretense that he's a corporate spy to help justify a continued security lockdown (also to swipe his security badge and make sure he's not in a position to need it). Out of nowhere, she randomly accuses him of having an account in the Cayman Islands. Much to everyone's surprise, he does — he's been infiltrating the company for years.
This sometimes happens on QI, when a panelist responds to a question with a joke answer that turns out to be correct. One of the best was this bit, upon being asked what the original purpose of corn flakes was:
Johnny: It was for, er, putting in mattresses, for monks, as, er, an anti-masturbation sound trigger device...
Stephen: Johnny Vegas... take some points.note As it turns out, he was only half-right: they weren't put in mattresses, but they were intended to discourage masturbation.
Johnny: You're joking!
Stephen: Now tell me something quite interesting about the original geishas.
Calvin: It's too darn hot out here. Hobbes: You could go wading in the creek. Calvin:(at the creek) This water is too darn cold. Hobbes: You could go sit in the shade then. Calvin:(sitting in the shade) This shade is too darn dark. Hobbes:(exasperated) You could go sit in your room with the windows shut and the fan and lights on. Calvin: That's what I was doing when Mom threw me out here. Hobbes: I was kidding.
EDI: Don't worry, Shepard. I only forget to recycle the Normandy's oxygen when I discover something truly interesting. Shepard: (Eye Take) EDI: That is a joke.
Done in Phoenix Wright: Ace Attorney during the second case. The day before his trial, Maya asks Phoenix is there's anything that she can do to help. The player is then given three options to say: "Defend me", "Be my cheerleader" and "Break me out of here". Whatever one you pick, Maya takes it seriously and starts to go to prepare for it, forcing Phoenix to state that "he's kidding".
Maya: Is there anything I can do to help? Phoenix: [Upon choosing "Defend me"] Alright, you can be my lawyer in court tomorrow. Maya: OK! Phoenix: Uh...? Maya: I'll rush to the library and pick up a copy of 'Law for Rookies'! Phoenix: W-Wait Wait Wait! I was kidding! It was a joke!
Aang: Maybe we can make some big pots of glue, and then I can use gluebending to stick his arms and legs together so he can't bend anymore. Zuko: (sarcastically) Yeah, then you can show him his baby pictures and all those happy memories will make him good again. Aang: (sincerely) Do you really think that would work? Zuko: NO!
Zuko finds himself on the other end of one of these in "The Boiling Rock":
A variant, from Foster's Home for Imaginary Friends: after an episode-long Running Gag re: Bloo's propensity for sarcasm, some random hobo-type guy tries to use "I was being sarcastic!" as a "Just Joking" Justification for being behind the shenanigan around which the whole episode revolved. Bloo and Mac are able to call him out, with extensive research to back it up.
In the Futurama episode "Love's Labours Lost in Space", when Leela seems strangely unwilling to ask Zapp Brannigan for help:
Bender: So what's the problem? It's not like you slept with the guy. (Beat) Oh... my... god.
Used in the Young Justice episode "Usual Suspects". Artemis and Super-Boy have just come clean about their secrets and less than savory connections, and the Plucky Comic Relief Wally sarcastically asks if anyone else has any secrets to share. The look on his face when Miss Martian steps forward...
It's worth noting that Lisa Ramirez, one of the conspirators in the Michelle Renee hostage situation/bank robberies, said during her confession that she had been the one to "jokingly" suggest that they rob a bank.
This Twitter exchange between some guy and Jason Scott, who is known for archiving tons of historical information about computers:
From X-Men, on a happy holiday to sunny Genosha, where Magneto is rallying his army...
Wolverine: "By my count, there are only a few thousand of them. Cover me — I'm going in." * Extends his claws*
* Pause. Wolverine puts away his claws.*
Wolverine: "I was just kiddin'."
Cyclops: "... Me too."
Dead Girl from X-Statix once suggested she was considering leading an army of the risen dead against the living. After a Beat Panel, she assured her teammates she was only kidding.
In Larfleeze, when the Wanderer and Stargrave discuss how they can infiltrate the Council of Ten's army.
Stargrave: If they're as confused and indecisive as you describe them, Madame, we can just show up and say "Reporting for duty as requested"!
Wanderer: Stargrave, you're absolutely brilliant!
Stargrave: No, I'm absolutely sarcastic! It was joke!
Wanderer: Joke or not, that's what we're doing!
In Star Trek: The Next Generation, Q loses his powers temporarily and ends up working for Picard. The local planet is in danger, and the characters are brainstorming to prevent catastrophe. Q mopes that if he had his powers he could change the gravitational constant. Geordi suddenly realizes that it might be possible for the ship to generate a force field that would have an analogous effect.
Data having No Sense Of Humour does this a fair bit; one memorable example is where Picard jokes Riker should be taken to the brig because of his actions during the episode. Data doesn't gets the joke and leads Riker away while he's protesting "Data he's joking, you know that right?".
Mal: If you can't do it from here, you put on a suit and get out on the side of the boat and... Wash:: And what? Wave my arms around? Mal: Wave your arms around, jump up and down. Divert the nav sats to the transmitter. Whatever. Wash:: Divert the...? Right. Because teenage pranks are fun when you're about to die! Mal: Give the beacon a boost, wouldn't it? Wash: Yes, Mal. It'd boost the signal, but even if some passerby did happen to receive, all it'd do is muck up their navigation! Mal: Could be that's true. Wash:: Damn right it's true! They'd be forced to stop and dig out our signal before they could go anyplace! (pause) Well, maybe I should do that, then!
Often on House, one of House's team will make a sarcastic suggestion that is hugely dangerous, bordering on unethical, whereupon House will say something like 'Well let's do that then' or 'That's just what I was thinking.' Once used the other way around, when House sarcastically snarls that since their patient is a kid they should cure her with puppies and sunshine. Which leads to Chase solving the mystery.
In the intro for the "VISTA" stage in Osu! Tatakae! Ouendan 2, shoe salesman Santarou Zaiko is getting chewed out by his wife for buying an oversupply of tacky, loudly-colored shoes. He tells her "It's not like we can sell them to aliens..." The next thing he knows, he's being shot into space to sell his wares to Venusians.
In the Saints Row: The Third mission "We're Going To Need Guns", on arriving in Steelport the Boss wonders where they can get a lot guns for the Saints' gang members, and Shaundi sarcastically suggests raiding a military armory. The Boss proceeds to take her at her word.
In Girl Genius, when Agatha is imprisoned, a cellmate says that she would have better luck having her clank try and unlock the door. Before the cellmate can stop her, Agatha says it's a good idea, gives the clank her lockpick (she wasn't having any luck), so it opens up the drain and disappears. Then the cellmate states that she wasn't actually serious.
A variation occurs in Lion King 1 1/2. Timon is unhappy with his life, and Rafiki tells him to seek Hakuna Matata, and to go beyond what he sees, prompting Timon to go on a journey to find a place where he'll be happy. The problem comes when Rafiki is talking Timon's mother later.
Rafiki: I told him to go beyond what he sees. Timon's Mother: Is that a metaphor? Rafiki: Well- Timon's Mother: YOU USED A METAPHOR ON TIMON?! Don't you know he takes everything literally?!
Gus in Recess is prone to delivering these lines: "What are we going to do, get the entire playground up here?" "What are we going to do, give everyone negative fives?"
In Donkey Kong Country episode Legend of the Crystal Coconut, after being told by the Idol of Inka-Dinka-Doo that "To Know everything one must give up everything" Donkey Kong wonders what he could give up...
DK: Little buddy, I'm giving you my tie collection!
Diddy: I think Inka-Dinka-Doo is looking for something more important than that, DK.
DK: What's more important than my tie collection?
Diddy: The Crystal Coconut, for one!
DK: (Gets Idea Bulb)' That's it! I have to give the Crystal Coconut away!
Diddy: (Mortified) I was kidding!
DK: I'm not. Once I give the Crystal Coconut away I'll know all the secrets, so I won't need it anymore. It's so simple!
Diddy: Who're ya give it to?
DK: Who else? (Cut to King K.Rool's lair)
In South Park, "Sarcastaball" starts with one of these. Responding to criticisms that football might be too dangerous for the kids, he ends up sarcastically describing a hypothetical sport (which eventually ends up with professional leagues):
Randy: Why don't we just have the players wear bras! And instead of helmets, they should wear little tinfoil hats, because it's the future, and we shouldn't be so barbaric! And while we're at it, we'll have a balloon instead of a ball, and whoever catches the balloon tries to run while all the other players hug! They'd love it! A sport where safety is all that matters? Why don't we call it Sarcastaball! I would love to be the coach of the Sarcastaball team!
Truth in Television: When Naoko Takeuchi came to her boss one day in the 1990's and said that she would like to draw a manga about a female superhero, the editor remarked: "Right. A female superhero. Maybe a schoolgirl at that, who is a crybaby, and yet saves the day?" And thus, Sailor Moon was born.
Behind the scenes of the Superman comics, Clark's wedding to Lois had to be held back in order to coincide with the event's occurrence in Lois and Clark. When the writers were talking about what to do in the meantime, one said "Why don't we just kill him?" He was kidding, but they did it. And it was awesome.
As you learn basically in your first week of Contracts in law school—this doesn't always work in court. A famous case has a guy (let's call them Alan and Bob) and his friend drinking at the bar when Alan starts talking about some property he owns, and (he claims) jokingly offers to sell it to Bob for a very low price. Bob, who thinks Alan is being serious (or so he claims), says, "Sure, I'll take that." The court found that Bob was honest when he said he didn't realize that Alan was joking, and so Alan had to sell to Bob for the absurdly-low price. The record doesn't show whether they stayed friends.
In 2008, the CEO of Doctor Pepper vowed to give everyone in the United States a free can of Dr. Pepper if Guns N' Roses released their album, Chinese Democracy. Not long after, Axl Rose said they were planning to do just that.
Al Jolson needed a theme song for the 1928 film The Singing Fool. Unable to find the right song, he asked songwriters Ray Henderson, Bud De Sylva, and Lew Brown to write one for him—on pretty short notice. The trio decided to create a super-sentimental clichéfest set to music as a joke, calling it Sonny Boy. They couldn't even bring themselves to put it in the mail box, and asked a bellboy to do so instead. Between sheet music, piano rolls, and record sales, Sonny Boy went on to sell three million copies—the only reason it couldn't qualify for going Platinum was such certifications didn't exist yet. According to Facts and Fallacies, "De Sylva, Brown, and Henderson laughed as they wrote the song. Al Jolson laughed too. All the way to the bank."