Yeah, I should have stated that better — I didn't mean literally asking the other person that question, but rather considering the question during (or better yet, before and after) the hostile argument.

Going on previous behavior seems to be a good guideline. Rather than asking, "Does this person hate people they disagree with?" you can ask, "How have they treated me in other disagreements? How have they treated others they disagree with?"

For instance, if someone has often been violent before over the (say) fifteen years you've known them, they will probably be violent again, and a new hostile argument might lead to an escalation of that violence. But if they have not been violent, they probably won't suddenly start being violent on account of a disagreement, even a nasty one.

For that matter, if someone is abusive to others (such as mistreating a coworker and gloating about it) then they might become abusive to you.