Have you added him to your blocked bidders list? If he is sending threatening emails through your personal email, report the abuse to his internet service provider (if it's yahoo, report the emails to yahoo. If it's AOL, report to AOL, etc.)
If he has been filing too many item not described disputes, ebay will limit his ability to bid/buy. It happened recently on ebay.com. The buyer filed an excessiving number of disputes so ebay put a stop to it.
I do not know if this will help but you might want to report them for feedback manipulation:
"Report members who are trying to damage your (or another member's) Feedback score or detailed seller ratings."
http://pages.ebay.ca/help/policies/feedback-manipulation.html
Have you add
Non paying buyers deserve unpaid item strikes.