So I'm chatting with this person [which I'm known to do]. The situation doesn't matter.
THEM: YOU have MS??
THEM: My [insert noun here] died of MS.
ME [out loud]: Oh my, I'm very sorry to hear that.
ME [silently]: And why exactly the hell do you tell me that, asshat.
Thirteen years after diagnosis and I still have no earthly idea how to respond.