Knock-Knock Joke

A common joke, told in the following format: "Person 1: Knock, knock

Person 2: Who's there?

Person 1: X

Person 2: X who?

Person 1: Terrible pun based on X."

The format does tend to make it annoying, as the second person usually wants to hear a joke, rather than be forced to participate. But it is possible to make them funny in the right situation. Because this trope is so well-known, it's subverted more often than not, by replacing the punchline with an unexpected insult instead.

A second subversion is when person 1 isn't actually trying to set up a joke, but person 2 acts like it is. Generally this leaves out the 'knock knock' being said, with person 1 knocking on an actual door.

The Other Wiki has an article on this plus examples, even prototypical ones from Shakespeare's time.

Compare Light Bulb Joke, What's a Henway?.

"Paulie: Knock, knock
 * In Paulie Shore is Dead:

Person 2: Who's there?

Paulie: Paulie Shore

Person 2: Paulie Shore who?

Paulie: Exactly"

"Dougal: Knock, knock.
 * In Police Academy 6, Hightower was fighting a thug, and the thug was getting the upper hand enough to tell one of these jokes. It was so bad, it ticked Hightower off enough to punch the guy out.
 * Father Ted:

Ted: Who's there?

Dougal: Father Dougal McGuire.

Ted: (Wearily) Goodnight, Dougal."

"Valentine: I'm sorry I don't have any books, puss, but I can tell you a knock-knock joke. I know the best one in the world.
 * Catch Me If You Can combined a subversion of this with a Precision F-Strike, to good effect.
 * From Mirror Mask:

Ravenous griffin: The best?

Valentine: You start.

Griffin: Knock knock.

Valentine: Who's there?

Griffin: ...

[Valentine escapes]"

"Knock-knock.
 * There is a book that claimed that this is the greatest knock-knock joke ever:

Who's there?

Interrupting cow.

Interrupting--

MOOOOOOOOO!"

"Knock-knock.
 * Dominic Deegan introduces a Crowning Moment of Awesome for physics students with a variant:

Who's there?

Interrupting static coefficient of friction.

Interrupting--

Mu!!!"

"Dan: Knock knock.
 * Then there's this one.
 * Also turned into a crowning moment of either heartwarming or heartbreaking in the movie Half Nelson.

Drey: Who's there?

Dan: The interrupting cow.

Drey: The interrupting cow who?

Dan: [has to think about it] ...Mooooo."

"Everything's backwards in Australia. They have summer when we have winter, all their teenagers idolize accordion players, and the punchline of all their jokes is "Knock-knock!""
 * And shows up in Ozy and Millie, but with an interrupting space alien.
 * Dave Barry referenced this when writing about the 2000 Olympic Games in Sydney;

"Stewie: "What's that you got there?"
 * From Family Guy. Stewie becomes unbearably nice once he has a near-death experience, so much that he tells Brian a knock-knock joke that ends with "your friend, Stewie, and he'll always be there for you." Brian retaliates:

Brian: "This is... THE most wrinkled piece of spider web."

Stewie: "What happened to the spider?"

Brian: "Knock knock."

Stewie: "Who's there--

Brian: "I ATE HIM!""

"Bill: Knock, Knock.
 * In News Radio, Bill tries out his new knock-knock joke on Dave:

Dave: Who's there?

Bill: Bill.

Dave: Bill who?

Bill: That's all I really have so far."

"Wakko: "Knock knock."
 * In Matt Ruff's Sewer Gas and Electric, in the afterlife, Abbie Hoffman is telling Ayn Rand a Knock-Knock Joke, trying to teach her about humor..
 * This gem from Animaniacs:

Scratchensniff: "Who's there?"

Wakko: "Max."

Scratchensniff: "Max who?"

Wakko: "Max wants to come in and go crazy!"

Scratchensniff: "See, that doesn't make any sense."

Wakko: "It does if you knew Max."

Scratchensniff: "But I don't know Max."

Wakko: "If you did, you'd be laughin'!""

"Queen Elizabeth: (knocks on door) Knock knock.
 * And now for a little subverting? First, 'Windsor Hassle':

Wakko: Who's there?

Queen: The Queen.

Wakko: The Queen who?

Queen: The Queen of England!

Wakko: It's not a very funny knock-knock joke ..."

"Snowball: Here's a little joke for you, Pinky. 'Knock knock.'
 * Second, with Pinky and The Brain, from 'Welcome to the Jungle':

Pinky: Well, that's not a very funny joke, is it?"

"The Brain: Who?
 * Once Snowball finds someone more receptive?

Snowball: The Brain.

The Brain: The Brain who?

Snowball: Exactly."

"Haley: "Knock knock!"
 * This Order of the Stick.

Crystal: "Who's there?"

Haley: "Roland."

Crystal: "Roland who?"

Haley: "Roland 'Itiative and his four friends Sneak Attack, Sneak Attack, Sneak Attack, and Sneak Attack.""

"Harriet: Knock-knock rook.
 * Studio 60 On the Sunset Strip:

Dylan: Who's there?

Harriet: Orange.

Samantha: Banana!

Harriet: Orange.

Samantha: Banana! It's banana! Banana, banana, banana! Then you say orange. "Orange you glad I didn't say banana?" Four-year-olds are telling this joke!"

"Deadpool: Knock, knock.
 * This dialogue from a Secret Invasion tie-in of "Deadpool''

Deadpool's Clone: Who's there?

Deadpool shoots the clone

Deadpool: And voilà!"

"Deadpool's Father: Who's there?
 * Another example with Deadpool. After telling his life story to a movie-maker, Wade knocks on the door of his long-lost father.

Deadpool: Wade.

Deadpool's Father: Wade... Wade who?

Deadpool: (pulling off his mask, revealing his scarred face) Wade until you see what happened to me, dad."

"Knock knock.
 * Played with in Bill Bailey's Tinselworm tour:

Don't say "knock knock", just knock! What's all this "knock knock" business?

I'm just trying to leaven the mundanity of your day.

Well, don't try to leaven the mundanity of my day! If I want my mundanity leavened I'll do what I always do.

What's that?

I will draw a moustache on the TV at random with a marker pen and wait for that glorious yet fleeting moment during the day when Jeremy Paxman becomes General Kitchener."

"Tiffany: Knock knock.
 * Subverted in the Discworld novel The Wee Free Men when Tiffany first visits Miss Tick, who is currently working out of a tent that has no actual door:

Miss Tick: Who's there?

Tiffany: Tiffany.

Miss Tick: Tiffany who?

Tiffany: Tiffany who isn't trying to make a joke.

Miss Tick: Ah. That sounds promising. Come in."

"Person 1: Knock knock!
 * Depending on your tastes, the following is either a case of Dude, Not Funny or Gallows Humor:

Person 2: Who's there?

Person 1: Amy Fisher.

Person 2: Amy Fis-

Person 1: BANG!"

"Knock-knock!
 * Ernie Steele of Backyard Sports does not use puns in his Knock Knock Jokes, but instead stops them in the middle. For example:

Who's there?

Heh heh! Nobody's here."

"WILLOW: I got her head back on, didn't I? And I got her off those knock-knock jokes.
 * The children's book Camp Knock-Knock is about a kid having a knock-knock joke challenge involving names, and getting stuck with the name Frederick Ornat.
 * Prarie Home Companion did a whole song based on knock knock jokes which is surprisingly catchy, and can be heard here with the jokes starting at 0:40.
 * The Buffybot tries for an epic one:

BUFFYBOT: Ooh, who's there?

XANDER: You know, if we want her to be exactly-

SPIKE: She'll never be exactly.

XANDER: I know.

TARA: The only really real Buffy is really Buffy.

GILES: And she's gone.

BUFFYBOT: "If we want her to be exactly she'll never be exactly I know the only really real Buffy is really Buffy and she's gone" who?"

"Wayne: They're so accurate they can just fly in through the door. It's like, "Knock Knock!"
 * Saturday Night Live, a 1991 Waynes World sketch from the first Gulf War. Wayne and Garth are geeking out over the new US smart-bombs and the novel first-person Night Vision footage on CNN.

Garth: "Who's There?"

Wayne: "Ka!"

Garth: "Ka who?"

Both: "KA-BOOM!""

"Dale: Knock knock.
 * During one of Mitch Hedberg's stand-up routines, where he talks about hotels, he says he likes to wear signs around his neck "so little kids can't tell [him] knock-knock jokes. 'Hey, how you doing, nephew?' 'Knock-knock...' 'Read the sign, punk!'"
 * A King of the Hill episode when the gang are at the alley after Hank cried in a romance film.

Bill: Who's there?

Dale: Boo

Bill: Boo who?

Dale: Boohoo Hank."

"Morte: Hey, Nordom... Knock-Knock.
 * In Planescape: Torment, with Morte trying to get Nordom to play the Straight Man:

Nordom: Why do you persist in addressing me as a door?

Morte: It's a joke, you stupid polygon. You're supposed to answer 'who's there?'

Nordom: I know who is there. It is you. Why would I ask a question when I know the answer?

Morte: You know what, just forget it."

"Knock knock.
 * The first movement of PDQ Bach's cantata "Knock, Knock," and its alternate version, "Sam and Janet."
 * An episode of The Mary Tyler Moore Show had Ted Baxter write his own knock-knock joke, but getting stuck on the punchline:

Who's there?

Anna Maria Alberghetti.

Anna Maria Alberghetti who?

..."

"Anna Maria Alberghetti in a taxi, honey, better be ready 'bout half past eight...."
 * He eventually comes up with one at the end of the episode that Mary thought was Actually Pretty Funny:

"Knock knock.
 * In the Community episode "The Science of Illusion" Britta delivers this Knock-Knock Joke in a Crowning Moment of Heartwarming after being called a Buzz Kill several times in the episode:

Who's there?

Cancer!

Oh, good, come on in, I thought it was Britta."

"Person 1: Knock knock.
 * In the Philippines, a popular variation is to replace a line in a song with a knock-knock joke. Popularized in a noontime show named Eat Bulaga! An example:

Person 2: Who's there?

Person 1: Riverboat.

Person 2: Riverboat who?

Person 1: Riverboat young when I first saw you..."

"Person 1: Knock knock.
 * A really bad Harry Potter related one:

Person 2: Who's there?

Person 1: You know...

Person 2: You know who?

Person 1: AAAAAAAAAAAHHH!!!!!!!"

"N. Bison: Knock knock!
 * A subversion from Kickassia, when N. Bison has Dr. Insano cornered:

Dr. Insano: Who's there?

N. Bison: GUN!!! {points a gun at Dr. Insano}"

"Michael: Knock Knock
 * Played with on The Office episode "Golden Ticket"

Pam: Who's there?

Michael: Buddha

Pam: Buddha who?

Michael: Buddha this bread for me (produces bread and butter)"

"Dwight: Knock knock!
 * Later

Michael: Who's there?

Dwight: KGB

Michael: KGB who?

Dwight: (interrupts Michael by slapping him) We will ask the questions!"

"Beavis: Knock knock.
 * From Beavis and Butthead:

Butthead: Who's there?

Beavis: Ura.

Butthead: Ura who?

Beavis: You're a buttmunch, dillhole, dumbass, and a turd!"

"Butthead: Knock knock.
 * Later

Beavis: Who's there?

Butthead: Ura.

Beavis: Ura who?

Butthead: Ura-ine. Urine."

""I like to float that one early to see how literate I can get with the audience...so I think I'll try some knock-knock jokes! Knock-knock!"
 * No actual examples, but in Angels of Light and Darkness, Suzie tells a stupid joke that isn't one, and John comments that her sense of humor is declining to the point where she'll be invoking this trope, next.
 * Dennis Miller in his 1993 HBO special, after a joke bombs early on:

"Who's there?"

"Nobody, I just like to wield that level of power over the audience. I say 'knock-knock', thousands of people say 'Who's there?'. It's the closest I'll ever come to Jonestown.""

""Who's there?"
 * One time in The Wonder Years, after an awkward silence between her and Kevin following a serious spat, Winnie signals her willingness to reconcile with a knock-knock joke:

"Sam and Janet."

"Sam and Janet who?"

(sings)"Sam and Janet evening...""

"Give me a Knock Knock Joke
 * Regularly featured as a segment on Lamb Chop's Play-Along, and honored with a song to boot.

Don't knock a Knock Knock Joke

They're always dumb

So tell me how come

After one I laugh and bubble up

After four I always double up?

Don't be an old slowpoke

Give me a Knock Knock Joke

Please!


 * knock knock jokes ensue*

That was a Knock Knock Joke

I love a Knock Knock Joke!

They can be awful, it's true

Still I'm telling you

I love a Knock Knock Joke

Yeah!"

"Brendon: (Shouting angrily) YOU KNOW WHAT!? KNOCK KNOCK!
 * An absolute classic from an episode of Home Movies, while Linda is giving birth.

Linda: WHO'S THERE!?

Brendon:"

"Zorak: Alright, here we go. Er, uh, um... Knock knock?
 * Possibly stolen from Space Ghost Coast to Coast:

Space Ghost: Um, who's there?

Zorak: (beat) F*ck you."

"Knock knock.
 * In Quest for Glory IV, this is your cue that you should NOT open a coffin, unless you have a ton of HP.

Who's this?

Yorg.

Yorg who?

Yorg Onnaregretitifyouopenthiscoffin!"

"Tim: Knock knock.
 * One episode of Hello Cheeky subverted this delightfully.

John: Who's there?

Tim: Oh, you've heard it..."