When your girlfriend's, or a friend who's a girl, or a female who walks by you, smells like someone opened a can of tuna coming from the vaginal area. It normally means she is in desperate need for a douche. Or a shower. And use lots of soap. Because that stench is hard to get rid of.
Two guys walk past a girl in Wal-Mart
Guy 1: DUDE! Did you smell that?!
Guy 2: Yeah bro. That was definitely a Flounder Bounder.
Guy 1: Hopefully she's making her way to the douching isle.
When 2 people who like someone fight for her "love". The person they are fighting for doesn't even like them back.
Jackson - Hey Bryce I heard you like Ashley
Bryce - Ya I also heard you like Ashley
Jackson - Lets fight for her love no balls
Ashley - Hey are you guys doing a flounder fight
When a man and woman are engaged in a doggy-style intercourse session and the man accidently leaves the vag and almost enters her knot. The woman then whips her head around causing both eyes to end up on one side of her head fiercely making eye contact with the would-be male intruder.
I was really getting into it with Beth - hitting it from behind. But I accidently pulled out and almost entered the back door and she spun around and gave me the Flounder Eye