Knee slappers 

When a woman has saggy old lady boobs that hang so low they slap her knees when she walks

I'd totally do your mom bruh, knee slappers turn me on

Knee slappers by JarMa13 December 3, 2018

the knee slappers 

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!"

the knee slappers by A knee slapper April 6, 2013

Knee Slapper slong 

A knee slapper slong is a penis long enough to slap against a man's knee.

Jaime is endowed with a knee slapper slong!

Knee Slapper slong by I, Wreckerrr October 13, 2016

knee-slapper

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*

knee-slapper by dont you just wish you knew July 13, 2009

knee-slapper

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.

knee-slapper by KROGO July 6, 2005

knee slapper 

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

knee slapper by Joe February 11, 2003

knee-slapper

A funny story or event. Generally used facetiously. If not used facetiously, the user is a dork.

AHAHAHAHA, that's a KNEE-SLAPPER!

knee-slapper by emelizabeth October 30, 2004