A day, any Saturday of any week, on which many college students wake up hungover (or still drunk) from the previous Fucked-up Friday, and begin to drink earlier in the day and continue all day and night. Sometimes, the drinking starts immediately after waking up.
-"Are you guys drinking beer at 9:15am!!??"
-"Haha, hell yeah, it's Shitfaced Saturday! We'll drink all day"