Videotape it and make copies so if they ever get their hands on the tape, you won't be left empty handed. See if this classifies as trespassing and see what you can do legally from there. I would even go so far as to call this harassment, imo. Then, confront the parents and, heck, I wouldn't even be scared to contact the school either. Depending on the principal, s/he might classify this as harassment, too, and you can possibly expel/suspend him. If you don't feel safe around this kid, your school has an obligation to rectify the situation (at least, that's how it is over here).