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1.
Acronym for "Hell yeah fuck yeah". Used in excitement and concurrence.
Dude A: "Are you going to the show tonight?"
DUde B: "HYFY mannnnn!"
by 40heaven November 29, 2010
 
2.
(Adj) The state of being Hyfy can either be good or bad.
1. Being extremely happy, excited, or anxious.
OR
2. Being extremely mad, pissed, angered, or frustrated.
(Good) A boy just got the best Christmas present ever, he is considered hyfy.
(Bad) Someone just lost a big game/bet and is in a very hostile mood, then he or she is considered hyfy.
(Bad) "Yo I'm about to knock this dude out, im so hyfy"
(Good) "I was so hyfy when I saw my new shoes"
by Kjolly January 20, 2008