Why would a woman behave this way?

There was a woman that a friend of mine used to work with was mean and nasty to him when she was around her friends. The woman acted weird when they weren't around. One time, when he looked at her, she smiled and winked at him despite her saying things like can, "I have the food in the containers today, hurry up" or asking where things were rudely. Why would she act differently when she was or wasn't around her friends?
Why would a woman behave this way?
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