A woman who is completely insane beyond the capacity of regular insanity, or craziness.
Glen Close in Fatal Attraction was a Bat Shit Crazy Bitch
Lorena Bobbitt was a Bat Shit Crazy Bitch.
Man 1- "That chick is gorgeous."
Man 2- "That's my buddy Dave's ex, she drove his own car through the front living room of his house. She's a Bat Shit Crazy Bitch."