Derived from the terms bro and skank.
Means a person - usually a male - who forgets/ignores his friends (brothers) for a member of the opposite sex. The person that the friends are being ignored for are usually sluts or 'easy'.
Guy 1: "Hey, you've stopped talking to Jack"
Guy 2: "Actually, he stopped talking to me."
Guy 1: "Bro skank?"
Guy 2: "Yup."