A knee slapper slong is a penis long enough to slap against a man's knee.
Jaime is endowed with a knee slapper slong!
by I, Wreckerrr October 14, 2016
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From (Or inspired from) The Tom Green song "Pet names for Genitalia"

A penis.
Because it slaps your knees, if you're horribly unproportioned.
Peggy Sue called me a Knee Slapper instead of a dick today.
by Springloaded June 6, 2004
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1) An otherwise unfunny, awkward, or just stupid joke. Usually a dad pun or something of the sort. Said after this to show that it should have never been said in the first place. Invented by hillbillies and rednecks when sitting on their porches, slapping their knees when somthing funny happens.


2)said after something funny and stupid happens.
1)
dumb guy:"Two peanuts are walking down the street, and one of them was assaulted!"

normal guy (slaps knee and fake-laughs):"Wow! That sure was a knee slapper!"



2)
guy skates and falls off rail, hurting his knee and friend laughs.
Later they are talking and laughing about a dumb joke.

friend:"wow that sure was a knee slapper!" (slaps knee)

skating
guy:"yea!"(slaps knee very hard, and dislocates it from the earlier accident)

friend:"no that's a knee slapper!"
by dhawk123 March 8, 2009
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/nē/ /slapper/

Noun

1. A joke; typically a pun or otherwise regarded “Dad-Joke”, the humour of which prompts an audible slap-of-the-knee from one or more of the parties involved.
Ron: “So me and the wife were down in Mexico last month, and she twisted her ankle at Salsa Night”.

Gord: “Oh no, what did you do?”

Ron: “I called ‘Nine-Juan-Juan’”.

*Audible laughter and slapping-of-the-knee*

Gord: “Jesus Murphy, Ron, you really had me going there for a second. Now that’s a Knee-Slapper”.
by be4nz1111 August 20, 2023
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A saying a person does when another person says an unfunny joke but you're being sarcastic about it, indicating it was the funniest joke you have ever heard in your life. (being sarcastic if you didn't get that)
"Hey Billy, why did the chicken cross the road?... TO GET TO THE OTHER SIDE!" *laughs hysterically*

"What a knee slapper, Timmy!" *slaps knee*
by lovelyleftorgan777 May 5, 2022
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Something so hilarious it makes u slap your knees. Funny moments that cause uncontrollable laughter.
My niece and I seen a man with a car dealership flag on his bicycle chased by a bunch of Chihuahuas, it was such a knee-slapper!! Hahahaha
by MainRain October 14, 2018
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When you cut your knees off and slap your partner with them
I was having a bad so my husband gave me a knee-slapper
by Unifart April 2, 2021
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