A group of nine friends who make weird jokes and react to them by saying "that's a knee slapper, har de har har" and slapping their knees.
Knee slapper #1"And then the whale said, wait whales can't talk!" the Knee slappers "That's a knee slapper, har de har har!"
by A knee slapper April 7, 2013
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when someone slapps their knees because somethings really funny.
eg. danas brother sings and dances to 'its raining men' KNEE-SLAPPER

eg. claudias hair is ranga *slaps knee*
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a joke that is so silly that in order to handle it you must slap your knee
Rick told me the best knee-slapper yesterday.
by KROGO June 26, 2005
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Sarcastically used to point out an unfunny joke. It originates from the act of slapping one's knee during vigorous laughter. Later took on a sarcastic meaning.
Comedian: I just flew in from Los Angeles, and boy are my arms tired!

Audience member in sarcastic tone: wow that's a real knee-slapper
by Joe February 12, 2003
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A funny story or event. Generally used facetiously. If not used facetiously, the user is a dork.
AHAHAHAHA, that's a KNEE-SLAPPER!
by emelizabeth October 31, 2004
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something that is stupid and funny at the same time
Guy 1: So a guy walks into a bar...OUCH!
Guy 2: ROFL THAT'S A KNEE SLAPPER! *slaps knee*
Random Guy: Oh yeah? How bout a face slapper! *slaps Guy 1 and 2's face*
by Skullex May 18, 2008
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adverb. A term used to describe a dumb-ass joke. Its inception was the result of someone noticing their friend slapping their thigh/knee when a joke was told. It's an official "knee slapper" when the person laughing sqints their eyes, slaps their knee, and can barely speak due the amount of laughimg taking place. This definition is considered a "knee slapper".
What do you call someone who doesn't fart in public?

A private tutor!!

-knee slapper
by MegDar September 21, 2009
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