When one finds something extremely amusing, while seated the person slaps their own knee in jubilation.
That joke was a hellava kneeslapper, I laughed my ass off.

by Count Funkula June 13, 2003
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Someone with a dick so big it slaps there knees while walking.
When ol boy pulled his kneeslapper out; she knew she was going to be walking with a limp the next day..
by lilsmarterthanaboxofrocks March 26, 2021
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The most extravagant reaction to something of funny, or toast-worthy nature, where someone uses their hand to make contact with their knee typically in a very absurd and flamboyant manner.
Guy: hey guess what
Guy#2: what?
Guy: UR MOM
Guy: performs a kneeslapper
by Toastingurmom February 27, 2018
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A phrase coined by a particular person who does theatre is lebanese and is super smart
THAT'S A KNEESLAPPER FOR SURE FOR SURE
*slaps knees wildly with a crazed look in her eyes*
by avamarie-is-super-pretty October 11, 2022
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An acknowledgment of a bad joke by slapping your knee in an obviously sarcastic manner. Antonym: kneeslapper. Synonym: dad joke.
HA! That's a good Polish kneeslapper, Chad! HA! Ha!! ha!!!
by Champ Liberty August 4, 2019
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A joke that's supposed to be funny but isn't really. And all you want to do is make the person not feel bad, but the joke isn't funny. So..... you just say "that's a real kneeslapper!"
Jim: Knock Knock.
You: Who's there?
Jim: Tree!

You: Tree who?
Jim: Tree Fifty!
You: THATS A KNEESLAPPER
by TheAwokenMyth April 12, 2017
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something you use when a jokes not funny but you want to make the person feel better about themselves.
friend 1:why did the chicken cross the road
friend 2:idk why...
friend 1:to get to the other side
friend 2's mind:unfunniest shit ive ever heard god damn learn some humor
friend 2:wowee what a kneeslapper!oh geez you really got me with that one!!!
by angelkitty June 20, 2023
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