It means to flip out or go a bit nuts, or to rant about something.
Katherine is going to go bitchcakes on Bill after hearing that news story.
When you call someone a BitchCake that means you can't just simply call them "bitch" they're far to hardcore-ly annoying to be a plain and simple bitch.
Dont say BitchCake lightly, even though it sounds so damn good, its offensive, make no mistake.
Unless, of corse, you are saying it in the sense you might call someone your bitch. If someone is your bitchcake they are totally yours for the spanking, BitchCake-slapping, and any other bitch related activities you can think of.
C'mon BitchCake! I need to get my freak on!