It is used to reference a terrible, horrible, no good, very bad day and is the summation of all the feelings of anxiety, angst and anger generally taken out at people who suck at life.
Something you say when you're depressed.
You aren't suicidal but you wish that you were because then maybe people would notice the pain you're confronted with daily. If you are suicidal, call 1-800-273-8255 it's going to be okay.
John: God please kill me
God: You don't mean that haha
John: I know but I could really use a hug right now