Is it illegal to shoot someone on your property if they have threatened you?

Question Details:

A couple of weeks ago I was out with a girl and her brothers didn't like it. So today her oldest brother's friend threatened to kill me if he ever saw me again and that he knows where I live. Would it be illegal for me to threaten him with a gun if he comes on my property being that he threatened to kill me? And would it be illegal to shoot him if he punches me being that he's a black belt in martial arts? Important Notice