Michigan drivers are not polite. Each state seems to have its own character of drivers. Michigan drivers rank amongst the most annoying because of their mid-western tendency to be passive aggressive. For instance, the turn signal is an indication for car behind you and in another lane to speed up to cut you off.
By contrast, in California, residents seem all too willing to drop back to let you merge with them. On the surface, this may seem like a good thing. But as I pointed out to a friend, I think it's one of the causes for their traffic problems. People merge poorly and inconsiderably because they can get away with it -- no matter how much someone cuts line to jump ahead in merging, someone always will let them in at the expense of slowing down everyone else. I saw numerous examples in which we didn't move for minutes because people were letting others who had decided not to wait in a given queue or merge when they were supposed to move in. In Michigan, those people would have been SOL. You don't merge, you don't follow etiquette and you're not going to get in. This discourages people from trying to "cheat" and get a little ahead at the expense of slowing down everyone else through a poorly planned merge or traffic queue.