Thoughtless perhaps, but I don't think this is enough to indicate arseholery. People often get very emotional about things and rant about people while still doing good things and behaving in an exemplary fashion most of the time.
I think it is indicative that not only is he an asshole, he's a asshole with violent tendencies.
I mean, I and everyone I know have become very emotional and ranted about things every so often, but never has expressing a desire to see people die a slow death entered into it. That he did says something important to know about him.
