As much as this seems like a real harassment to the OP, site rules forbid player warning.
The best course of action would be:
1. Report him for harassing. This one is a very serious infringement and as far as i know, STF dont neglect those cases, they will work to deal with that guy, most likely banning him.
2. Never, EVER reply to a wacko. Those guys wants attention. Nothing frustrate more an offender than completely ignoring it. Also because there is really no point talking anything with someone lacking that much self control.
It was a mistake answering him once. It was another major mistake bringing this drama for a public site. Now you allow him to harass you in game and also in this site.
You gain nothing and just got more exposed in the process.
Sorry, this thread is dumb and mods need to nuke this, for your own sake.