The physical reaction on someone's face, and in particular the involuntary contractions of the lips that occurs when an individual becomes extremely jealous or envious when hearing about the successes of others (family, friends, rivals, enemies) - usually this facial expession precedes a petty or otherwise disparaging comment. Often accompanied by the act of "Casting shade". See also - "Flounder Mode"
1. "Did you see Victor's face when Jimmy pulled up to the house in his brand new ride. Chrome was gleaming man. Yeah Vic got dat Flounder mouth real quick when he heard it was paid fo wit cash! "

2."Ohhh did you see last night !!?? Becky stay in Flounder Mode all night when she found out that she was actually the third round draft pick for Johnny. She was talking shit all night after he pulled the whole switcheroo right after they arrived at the party for a hotter chick. Dunno why she fighting so hard to swim upstream. She know she basic"
by Street poet December 28, 2019
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A yellow flounder is what infantrymen in the vietnam war called the local prostitutes, referring to their race and lady parts.
"Boys, I'm going fishin' for some yellow flounder"- Mike Hunt 3rd infantry division member
by Moy Roore January 10, 2018
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For one to have intercourse with a third-wheel.
John should have a sweet night, said he'd even have a go at pounding the flounder! Prim 👌
by TheFlameBurnsWickr February 24, 2016
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