Anything that threatens ego, so long as I am attached to it.
Ego is all about being on top... about surviving... about being right.
Even the suicide perpetrator commits self-murder only to be right and to show everyone else how wrong they are. It is an act of separation -- denouncing ties with all those unworthy to be in the same universe with them. In a very twisted way, suicide is a form of "survival" -- of having the "last laugh."
Without ego, one is no longer vulnerable. Anything can happen and stress doesn't have a foothold. Like a ghost, everything passes right through us. Only when we become attached to something as important -- hold onto some reason or some "because" -- do we become solid enough to feel the slings and arrows of outrageous fortune.