How do i report this lame player?

I was Griefed by a Random Player.
What do I do now?

Okay,
This is not a bannable offense. It's a legal 'tactic' according to A-Net. They are called Griefers. Search the term. Several debates on them.

Reporting people. Go to Guild Wars Support found at the official site. Or search for them here

And NO POSTING NAMES! Please.

-Closed-