What are some synonyms for 'rare' or 'unusual' that have a negative connotation. For instance:
Enron's collapse was unusual, as the massive financial trickery ultimately bankrupted millions of investors.
What could replace 'unusual'?
I think Aberrant may be my top choice, perhaps merely on account of it containing 'err', in this context. Others that may be appropriate depending on the emotion related would be:
Adj: Deviating from what is normal or usual, typically in a way that is undesirable or worrying.
Adj: Having a harmful effect, especially in a gradual or subtle way.
Catastrophic: While Enron's collapse was certainly bad, catastrophic might be a bit over-blown, depending on what point the writer is trying to make.
Ruinous and disastrous may be slightly weaker than catastrophic and devastating.
While all these possibilities do not explicitly mean "rare", I think most people understand that disastrous events are rare by their very nature.