Report them to eBay. Unfortunately, the only way around this is to list your items for auction so you can choose to cancel off the bids of a buyer you don't want and then block them. Obviously youve got some idiot who thinks his behaviour is amusing. If you do a buy it now, they can bid and then you're stuck with them as the buyer. I really wish eBay would tighten up on the registration process so that kids and troublemakers can't just make accounts and the be the bane of everyone's existence. And you ignore people you don't want to converse with and you only ever use eBay as your point of messaging. Forward the nuisance emails to eBay. They've got the resources to track IP addresses, they should use it to stop this jerk. Sorry you are having a bad time, most eBay buyers are like me, nice, honest decent folk who bid responsibly, pay quickly and dont cause hassles. People should realise that eBay access is a priviledge, not a right and if you act badly, you should get banned permanently.
Ebay buyer more than 10 years, over 1,000 purchases!