Tiny Kneecaps 

Having tiny kneecaps means you have a big dick

“Damn, you got some tiny kneecaps.”
“Must mean you got a big dick.”

Tiny Kneecaps by Richard The Science Guys December 18, 2018

seahorse kneecaps 

A term you call someone or something that is useless

Fred:hey Jim can you help me hook up with this Jacob twiggs

Jim:nah I'm good fam

Fred:you're about as good as some "seahorse kneecaps"

seahorse kneecaps by PrapyJhonsPiza April 24, 2017

Buckling Kneecaps 

When the dick is so good your Kneecaps buckle.

Josh pounded me so good he turned my knees become buckling Kneecaps.

Buckling Kneecaps by Marchioni May 6, 2020

Eat your kneecaps

When one falls from a great height (presumingly in a video game) and "eats shit" with a knee to face connection.

Also commonly:
Ate my kneecaps
Ate your kneecaps
Eat my kneecaps

I was playing COD4 with you yesterday and watched you eat your kneecaps

Eat your kneecaps by Chief Netic January 13, 2014

Say Goodbye To Your Kneecaps 

A good comeback for when an asshole is making fun of you for being short

Asshole: You're so short lmao, you can't even hurt someone!
Person: Say goodbye to your kneecaps, asshole.

Say Goodbye To Your Kneecaps by StarShiningAgain October 30, 2019

Tiny kneecaps 

You have a large dick

Example
Man: y'all got tiny kneecaps
Other man: yeah all the nutrients went to my massive dick

Tiny kneecaps by Big Mind December 19, 2018

hit them kneecaps 

Perform oral sex to someone

I took her to the club last night, and when we got back to the crib , she hit them kneecaps .

hit them kneecaps by Lonesomelife October 9, 2017