Flowerpot coral, (goniopora) is one of the many that should not be harvested due to a horrible survival rate. SOME people manage to keep them alive for a while, most die within a couple of months. Carnation coral (dendrophylia) is another beauty that is doomed to die in our tanks...
That being said, IME, mushrooms can be almost impossible to kill once they're established in a tank, so my vote goes there...