When you can't remember what day something happened, because you've been awake for too many consecutive days.
Person 1: Remember that party yesterday... wait, or was that this morning?
Person 2: I don't even remember anymore, it was yestermorrow.
Person 2: I don't even remember anymore, it was yestermorrow.
by TheReminder June 13, 2011
by TheReminder June 13, 2011