When someone, typically a woman, is in a mood where everything either bug her, irritate her, get on her nerves, or all of the above. They will then, eventually over time, lash out to those who listen and the wraith of their bitchiness will turn to you. You are then, inadvertently, the target of their bitchiness.
I didn't do anything, I'm just listening and agreeing with you. Why are you attacking me? You must be in a bitchmood.