"for no apparent reason "
exactly. none of us were there. I know it was your sister, but from ONE persons side of the story everyone is making it out like he is the villian. Maybe he is, maybe he isnt. But really, unless any of us was there, or the guy driving the Falcon turned up on the posts to defend himself, none of us can sit here and say he is totally in the wrong.
Reading your first post, looking at it through the eyes of a reasonable driver, I'd suggest that there isn't all the story being told. Im not saying he isn't in the wrong by getting out and abusing your sister [no matter what happened, he doesnt have the right to do that], but come on, she was 'just' minding her own business and all THAT happened. I doubt it very much. Either your is in her own dream world when she drives and didnt see what she did wrong for him to go off at her, or she isnt willing to disclose the full happenings of the incident.