-To quack is to perform an act that displays one's stupidity, incoherence, lack of coordination, or outright inability to relate or adapt in a social setting. Derived from the sound a duck makes, more specifically the verb form for what a duck (see definitions 5,8, and 9 for "duck") does.
-To fuck up the situation for everybody.
You missed the biggest quack!
What happened?
____ ran down the hill, tripped and busted ass all over the sidewalk and fence by the tennis courts!

How was your birthday?
Fun as shit, we got fucked up then ______ quacked ridiculously by hitting the blunt BACKWARDS! He didn't even notice for like 2 seconds, then he got up and slid down the hill and lost his keys.
What a fuckin' quack

I dropped the entire pizza on the ground.
You're so quackin.
by DaQuackyPaki December 7, 2009
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noun: slang for "crazy" common in the south, especially near areas of high duck concentration.

1. That's quack, man.

2. You're so quack.

3. Dude! that's quack, yo!
by thats whack February 23, 2009
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1. The act of pulling down a beanie-hat hybrid over someones face to where the bill of it is over their mouth, hence the quack.
Bro: dude that nerd is way to nerdy to wear that cool hat.
Bro2: I know dude. Let's quack him.
...
Nerd: Ahh noo. I've been quacked!
by SEV3N November 8, 2011
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Quacking is a term which refers to the loud guttural sound which reverberates from a females esophagus as a penis is thrust into it and then removed forcibly creating a suction-force induced sound which resembles the characteristic harsh sound uttered by a duck.
"Yo dude !! - I fucked that bitches throat so deep and hard last night she was quacking! :"GWACK GWACK GWACK GWACK!!!!!!!!"
by Dr Seymour Butts November 20, 2012
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Quack is a word that can mean many things. It is the sound a duck makes, it can be an insult, & it can be a punch line.
Duck: quack
Angry human: what a quack!
Funny human: your just quacking me up!
by NoodleQuack February 19, 2018
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Quacking; to be afraid of something like a duck after a gun is shot.
“I’m coming for your job mate.”
“Oh no I’m quacking!”

“I’m quacking at the thought that our president will ruin this country.”
by xJimJam May 14, 2019
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