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.
by BlooPenguin March 27, 2007
Chaotic, out-of-control, insane, crazy
Everyone is going totally bitchcakes today!
by Derek B. December 11, 2003
When Joan's boyfriend didn't come home for 2 days, she went totally bitchcakes.
by kat August 13, 2003
An emotional, predominantly female state of being characterized by overt displays of anger and emotion. Often associated with PMS.
I cmae home late last night with no good excuse. Man, did my girlfriend go bitchcakes
by monkeyman1968 July 18, 2012
Exclamation of joy, anger, or confusion. Nickname for friends. Or a HUGE diss.
Hey bitchcakes, get me a soda!
by P-dawwg June 15, 2007
An extremely attractive female, possibly bitchy and dominant; may attract to those of the bitchrake kind.
"The chick I was tiger-lilying turned out to be one heavenly bitchcake!"
by Dickcheeseburger! July 5, 2006