when a girls hair is incredibly unkept because of going to sleep drunk after a night of partying. not uncommon is to find little pieces of food and clumps from drooling while sleeping.

this most often occurs on friday after a late thursday night but the girl is to lazy to do her hair because she knows she will have to when she goes out again later that night.
tony: omg look at that coke addict, she looks a little like sara, that whore deff has aids

rachel: no, that IS sara, looks like shes suffering from a case of friday hair
by itaub1 May 19, 2009
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It's Casual Friday to the next level, where people come to work without fixing their bed hair.
Joe: "Whoa, what's with your hair, dude? Rough night, last night?"

Bob: "Didn't you get the memo? It's Big Hair Friday!"

Joe: "Gee, I can't believe I forgot it's BHF!"
by GeekSquadRejects March 11, 2010
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When a hairy man decides to let loose on a Friday happy hour, letting his chest hair out in public so the bitches come flocking. The primary goal of this move is to get laid. He's kept it hidden all week but when work ends on Friday, it's Chest Hair Friday!
You see your buddy at the bar on a Friday night, chest hair out in the open, and he's talking to a girl. You come over and say, "it's Chest Hair Friday!"
by Chesthairfriday July 3, 2013
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