A day in which you wake up feeling completely apathetic towards everything so that every response that you give is around the lines of "does it look like I give a fuck?"
Person one: dude I slept at 4 am doing my spanish homework
Person two: :'(
Person one: yup today was a complete fu day, you should have seen the look on my sisters face when I told her to fuck off when she asked about my opinion on her wedding. Priceless... :)