Possible Duplicate:
Create a blacklist to keep from seeing certain users.
One user in particular is being very aggressive, negative, and simply wrong. Can I block this user from my question?
Possible Duplicate:
Create a blacklist to keep from seeing certain users.
One user in particular is being very aggressive, negative, and simply wrong. Can I block this user from my question?
You should definitely flag the problem posts for moderator attention with an explanation, since we don't tolerate hostile behavior.
See related discussion and user script:
(browse the "linked" sidebar on that page for the discussion)
You cannot do this. However, you could write a user script that hides answers and comments from those users.
If someone is aggressive, flag or discuss him/her on meta. And don't forget any nessecary downvotes!