Blizzard most certainly takes harassment seriously. They have a whole write up on it to help folks who feel they are being harassed. There are quite a few tools at the disposal of players to mitigate it on their end, and to report it to Blizzard.
As others have said, put them on Ignore and never reply. If they circumvent Ignore, take note of that - name, server, chat channel, time stamp, nature of communication. Report for Ongoing Harassment via ticket.
To be clear though - this is NOT considered harassment. This is an open world MMO. Other players have every right to stand wherever they want, whenever they want. Silently standing there violates no rules.
They can not verbally harass you, they can’t bring a mob and disrupt your RP event. Those things would actually be against the rules.
Standing there though is not against the game rules. It is like the annoying sibling going “I AM NOT TOUCHING YOU!!” Except in this case the player is not speaking or communicating at all. Super annoying, but not considered harassment given they have the right to be there too.
You do not get to decide who can be in which areas of the game, and when. If you don’t like someone standing there, you need to move the event to an area that you control such as instanced content. Others have had some great suggestions for that.
If you would like a Blue opinion on the subject, use the pencil edit button on your first post. From the edit drop down menu change the forum from General Discussion to Customer Support. I am sure Vrak or someone can clarify for you just what “harassment” is and if standing there is punishable.