Currently, to ignore posts from a user, you have to go to your BBS profile, edit your Personal Messages options and put user names in your ignore list.
I realize this is a function of the BBS software, but it would be nice to be able to do this by having an "ignore posts from this user" link on the message you're reading. There is currently a "report to moderator" link, it would be nice to also see a link to ignore the user.
I have never squelched or ignored anyone in-game on here on the BBS; I find it a good source of humor - plus I generally have the self-control to not feel the need to reply to every message and get dragged into arguments.