First off, I'm going to say that I'm not going to advocate being a jerk towards anyone. There is never a cause to be rude or abusive in our responses.
While we obviously shouldn't be rude or abusive, I don't think we should walk on eggshells either. Sometimes a topic is about bad behavior on the part of querent. Any question starting with "Was I unprofessional when I..." is going to have answers that are a resounding "Yes" as at least one answer.
If someone is engaging in self-destructive behavior, such as in case:
I've killed my colleagues' characters during RPG session, now they won't talk to me
Or if the OP was just asking a question on how to engage in bad behavior such as in this case:
How can I deal with troublesome Professional Engineer?
IMO, both of these cases, the querents simply acted badly.
so, I was wondering:
How careful do we need to be to avoid making a poster feel bad when a querent is asking about their own bad behavior?