This song is about a girl, who gossiped and spread fake rumors making her a backstabber. The protagonist tells that she was tired of the girl who kept on lying about her. The girl was lonely,so she started gossiping so that she would get attention. "Now I know, exactly what you're all about. What I'm all about? This is what you're all about!"
The above lines say that, the protagonist is tryna confront the girl. "Girl, you're such a back stabbed, stabber. You're such a backstabber. Oh girl, you're such a shit talker and everybody knows it everybody knows it"
This is maybe how she confronted her. She maybe revealed about her making fake rumors to end her "loneliness".

This is just my theory,
Anonymous