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3.
Fuck - It - I'm - Young

Justification for doing anything immature, stupid, dangerous or ridiculous
Jimmy: I dunno man, do you really think you should fuck this dead hooker we found here in the forest

Billy: FIIY

Jimmy: Hmm didn't think of it like that, Seems legit
by SmilesNLulz May 27, 2012
 
1.
fuck it i'm young
more commonly used on the internet that in real life.
online conversation-

friend- you out tonight?
me- i wasn't going to but fiiy!
by Bethany-Ruth July 07, 2012
 
2.
The acronym for the phrase 'Fuck It I'm Young'. It's infinitely better than YOLO and much easier to pronounce, obviously.
Matt: You shouldn't eat pumpkin soup whilst recording the podcast mate
Cailem: FIIY
by Steven. Just Steven. August 17, 2012