an insult or a threat that one tells to someone else. once the person who replies with "who's there?" the ejoke abruptly ends with the answer "fuck off" many opther endings can be used to make this insult more interesting or more focused on the insultee.
"hey, knock knock"
"who's there?"
"fuck off!!!"

"hey knock knock"
"who's there"
"a fuckin dick thats about to get their ass kicked"
by Ratbiker May 23, 2007

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Top Definition
Epic joke told by character Carl Hanratty (Tom Hanks) in 2002's "Catch Me If You Can".
Carl: "Want to hear a joke?"
Bill: "Sure."

Carl: "knock knock."
Bill: "Who's there?"
Carl: "Go fuck yourself."
by Holloway11b June 26, 2010

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A fun game in which the participant stands outside a closed door where someone is sleeping. The player pulls out his penis and begins to masturbate. He must stand close enough to the door so his hand knocks on the door as he masturbates. The aim of this fun game is to get off before the sleeping occupants wake up and come to see what all the noise is. While the player technically loses if the occupant comes out of the room too early, the player may be able to get sex out of the occupant should it be an attractive female.
Guy 1: Dude I'm bored. What can we do?
Guy 2: Well we could always play knock knock.
Guy 1: Alright but this time I'm not going to my mom's door.
Guy 2: Fair enough.
by oh tee gee May 15, 2008

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Popular children's game derived from William Shakespear's "Macbeth" - Act 2, Scene 3, line 7, "Knock, knock! Who's there, in th'other devil's name?.."
Knock knock?
Who's There?
Hooh.
Who hooh?
No im not an owl, im Hooh.
by MadScientist February 24, 2005

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slang for Jehova's Witnesses. Due to the fact that they come knocking on your door almost every damn saturday morning when ur trying to watch cartoons or eat breakfast. They feel compelled to interrupt your important free weekend morning by telling you about how god loves you and such.
I was beating off to some ill ass porn, then the knock-knocks came callin and I had to put the beef away. I got pissed, drew a pentagram on my forehead and answered with a massive boner, informing them that I had found solice in satan and blasphemy. I asked them if I could get back to having sex with this downs syndrome girl I had picked up at the bus stop. They haven't been back since.
by Destructive Criticism April 27, 2005

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"Knock. Knock." Is a term used primarily by hackers and they send them to their victims who they are about to swat usualy on Twitter or private message.
Knock. Knock.
by Sock pen September 30, 2016

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Term used by the BSP crew when refering to anything negative. Mainly used when no other term will suffice.
God damned fucking mother-fucking knock-knock as fucking knock-knockhead
by gesis March 21, 2003

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