What I would like to see is a “Reverse Ignore” option. That is, I want to put some other specific user on a shit-list, whereby that user will not see anything that I post.
Thus, if some other user takes umbrage at something I wrote and snarks at me (or worse), I would like to black-list that user so that he never sees another of my posts. (I might still want to see that user’s other posts on other subjects in other threads, or I might want to Ignore in both directions.)
The person you want to bar from seeing your posts need not be logged-in to read, so there would be no way to ban them by username. Doing it by IP address might be theoretically possible, but is more complicated and comes with its own limitations.
I agree with John Mace. Plus, it’s a public board. If you post here others have the right to see it. If YOU choose to customize the board so that you don’t see certain posts that’s fine and doesn’t take away from the rest of the board, but controlling what other posters see doesn’t seem right.