Once time a few years ago I looked over my shoulder as we prepared to merge right and exit the highway. I saw a truck zooming up from behind and shouted. While we didn't manage to completely avoid a collision, it only sideswiped us. I used to try to remember which drivers didn't like it when I would double check and would would avoid it with them as a way of showing respect, but now I see slightly decreasing our risk of collision as also a form of respect.