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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
 
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