Serious bullying and trolling are considered as violation of forum rules so you can use the report to moderator button if he do that in his posts and when he sends you PM then you can use report to admin feature.
Better consider the user to be on your ignire list.
There arent so many things that really annoy me like a bully and this counts for a online bully too.
As someone who was bullied most of my life for things out of my control, I feel sorry for you.
This is what you should do the next time he is mean to you. But use the ignore feature on this site to relieve yourself of these messages.