Internal company policy that mandates that you log off and stop working at 5pm on Fridays and that do not start back up on work until Sunday, when you're prepping for the new week.
(Coined by the co-founder of the tech start up, Yogi.)
person 1: "damn, I'm so burned out from all these late nights."
person 2: "yo, don't worry, it's Fuck It Friday today, just go home."
person 1: "I love Fuck It Fridays!"