Thanks, and I just want to say that I think your advice to Sarah was compassionate and well crafted--good communication about communication!
How to act with this person?
I think your words about "forging an agreement about boundaries" are good in any situation, and are applicable in this thread, also.
What if we all forged an agreement to speak about issues and withhold negative judgments about personalities and peccadilloes?
Ad hominem arguments are generally seen as exposing the weakness of one's reasoning on an issue, so swearing off them is just agreeing to stop shooting oneself (and one's cause) in the foot.
That hardly a great sacrifice, it seems to me, and especially not considering the intelligence level of this forum, and its potential for really great clean debate.
I suggest we agree on boundaries and proceed from there. Does that sound reasonable?
PS: Glad you like the pic.