As said above :
Technically, Client side, it is likely possible to hide them.

But :
- I doubt SE implement something to avoid matchmaking for raid clears and so
- It will never prevent people to create alt(s) to troll or harass (or worst, to team up to troll or harass).

Unfortunatly, stalkers and troll are what they are : it's a problem of personality and education.

As soon as they are going too far, the only way is to report them.