It is an addon that can announce to any channel of choice:
for Warriors: whenever taunt is resisted, or mocking blow fails, whenever you use Last Stand, Challenging Shout, Shield Wall, or Lifegiving Gem
for Druids: whenever growl (druids) is resisted, whenever you use challenging roar
for Paladins: whenever Righteous Defense is resisted.
Furthermore, it can remove any buffs desired, either always, or only in defensive stance/bear form/with Righteous Fury active.