When a person's body/brain goes into overdrive and continues to push forward without stopping until they are done. 1) Notorious among college students pulling all nighters and 2) partygoer's that are down to do anything.
1) I have a test that I have to study for and a project that is due tomorrow...time to enter fuck it mode.
When someone gets pissed at the rest of the world because they decided not to finish what they started and then depreciate themselves by getting stuck in Fuck-it Mode.
Dude, why is Lori so butt sore? Don't mind her, she's lost in fuck-it mode.