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A phenomena in which when a group of nice, normal girls all turn into bitches because a bitch decided to socialize or spend time with them. There is no guarantee that the, initially normal girls will revert back to their non-bitchy selves after the after the initial bitch turns them into bitches. It can quickly spiral out of control so take extreme caution when you know a bitch is going to be at a social gathering.
John: God damn it ever since Lizzy met Cassandra she's been such a bitch.

Julia: That my friend is what the Bitch effect is.
by Suijinheki October 21, 2010