They thrive off of being your best friend by day, sleeping with your bf/gf by night. Also often they use privileged information gained throughout a long term relationship in order to try and smear your reputation.
She helped me plan my going away party and then slept with my bf when I was gone! What a Mac Stabber!!
After 3 years she lied to the cops and had me arrested for DV, Audrey is such a Mac Stabber!