On your User Control Panel, under "Friends & Foes":
Manage Foes
Foes are users which will be ignored by default. Posts by these users will not be fully visible. Personal messages from foes are still permitted. Please note that you cannot ignore moderators or administrators.
As much as possible, myself and the moderator team try to maintain an open board within the context of the posting guidelines. It's a convention guaranteed to infuriate many members at one time or another, or a few members many times over, but IMO it's the fairest, though hardest, way forward for the board.
Members who frequently find themselves infuriated by another's contributions should consider whether the "foe" function could make their RI experience more palatable.