After midnight of every day. Technically it's the next day, but doesn't the next day really start when you wake up in the morning? Therefore; anything happening between midnight, and before you go to bed doesn't really fall into a proper day's definition, and technically never happened. Particularly useful while partying all night.
We were so shit-faced we nailed a picnic table to the neighbors house at 4am last night. Technically, that never even happened cause it was on noday.