Past the point of insanity, past the point of rationality. Incorperates both the meanings batshit and loco but on a much higher scale. Just losing it, the day before or maybe the day you are commited permenantly to a mental asylum.
Jim: Yo dude, whats up?
John: Not much, dave's nailing hamsters to the wall in the kitchen
Jim: WTF?!? what for?
John: His girlfriend left him for his brother, He's gone completely fucking batshit loco