Most likely this has been suggested before since this script exist, (i don't have access to forum search).

[REL] New Ignore Script! (Author: Blam) <- details; and better descriptions of needs and reasons, there.

• "/ignore <name>" as a toggle command, unignoring <name> the second time if used as same argument.
• "/ignorelist" shows currently ignored users
• It would (should) block room chat, private messages and em/emote coming from the ignored user

The drawback of this script seems to be it needing a separate auto-loader script, unless manually loaded; and whether or not it covers pm's and em's. (and having to *google* this forum, just to find it's magnificene ).