Not British slang...it is from the 90's TV show "Newsradio". Secretary
Beth decides to make up a word and see if she can get others to use it by dropping into every conversation. By the end of the day, everyone is using it. Has become
popular in Britain due tothe popularity of the show.
It means to flip out or go a
bit nuts, or to rant about something.
Beth went completely bitchcakes when she found out Matthew told
Joe they were sleeping together.
Katherine is going to go bitchcakes on Bill after hearing that news story.