To tell someone to get away or to leave, usually in an unfriendly way.
Beatrice: Jim, I want to talk to you. I haven't seen you in a while. How have you been???
Jim: Well, I don't really want to talk to you Beatrice. You dumped me and left me for dead in the park with a broken heart, you know; and thanks to that, I'm seeing someone else now. Be Gone!!
Beatrice: Jim, no wait.....I really want to see you again, I'm sorry about everything.
Jim: Too late Beatrice!! You had your chance, and you screwed it up!!
Beatrice: JIM!!! (screaming)
Jim: Do you not understand English??? "Be Gone" means get away, now leave me alone. I'm on my way to see my new girlfriend now.