It is subjective. Offense is subjective to the reader.
Each person should have the right to communicate according to their ability or preferred style.
If said communication infringes on someone else's privacy, freedom, or safety then it is up to the community to call bullshit.
For example; if someone posts another pesons personal messages without their consent then they have infringed upon that persons right to privacy.
This has happened in the past. Though not to often. The responsibility that odeon talks about, I think, is about moderating our own behaviors so that we do not cross that line. If a person cannot moderate themselves (I understand this because I have impulse control issues) then it is up to the rest of us to point out how such behavior is wrong.
If the perso does not get it, then the community should call them on it, repeatedly. Make them feel unwelcome. If that does not work the they are just a troll looking for attention. The best way to handle a troll is to ignore them.
Personal attacks are ok, IMHO, if that is how you choose to communicate a point. Although, if you do the others will learn to blow you off as irrelevant.
You seem to be lost in your own thoughts.