The top definition from UrbanDictionary.com has this to say about "massholes":
1. For residents of Massachusetts, it is an achieved title for drving faster, being wreckless, cutting other drivers off often, and having no patience for other drivers on the road.
2. For non-residents of Massachusetts, it is a term of dislike for the people of Massachusetts that drive like an asshole.
In short - many residents of Maine, New Hampshire, New York, Vermont, Rhode Island, and Connecticut feel that all residents of Massachusetts are massholes. You don't mind that, right? Because by becoming a resident, you'll probably pick up some of the habits chronicled on this site.