As in ....you post something you feel is rather innocuous, or sincere, or perhaps revealing something rather private and honest and candid, and someone blows you away with a nasty comment?
I am not speaking of heated debates. If one participates in those, one expects to receive passionate replies which may sometimes hurt. I am not often offended by those.
I'm speaking of just out of the blue hearing something totally off the wall and hurtful in response to something sincere you have written.