In my opinion, this is the most needed and the biggest missing feature in XF right now. I hunt for this add-on weekly. I have a troll that everyone is clamoring to have banned, yet he really doesn't break the rules. he's pretty clever, actually. XF needs a "Tachy goes to conventry", or "global ignore" or Hellban option, desperately.
I'm quite surprised nobody has produced the add-on yet.