he doesn't know my real name. The guy also attacks other people on the site. People like him is looking trouble.
It takes 2 to argue or fight. If you totally ignore him, he should soon tire of not getting a reaction, and move on. Some thrive on conflict, and when they don't get, they get bored.
In the meantime, be very aware of what's going on around you. I'd file a complaint if he made a threat, but be aware than the police may no do much, if anything.