I recall my worst experience, it was also on The Forgotten Coast realm horde side. This guy was stalking me in 1K and even waited for me when I would log off, eat dinner come back on. He tailed me forever until he got a response from a GM, I could tell because he tried to reply to the GM in /say instead of /tell. After his conversation with the GM he broke off and then attempted to KS me multiple times and I threatened to report him for the harassment after which he let me be.

Many people are convinced that they know whats right and wrong and take it upon themselves to met out justice even though there are GM's to take care of such matters. Just follow Gadzooks advice and record the incidents just in case you need to report them later.