In the USA, there are two North-eastern cities, which are rivals on many counts, and who are considered to have some of the worst drivers - Boston and New York City. In an effort to both expound upon and narrow-down lordaych's very accurate and thourough write-up, I'd like to discuss my theories on these two notorious groups of drivers.
Simply put, the main difference between the driving abilities in these cities is such: New Yorkers are generally highly skilled drivers, they are just choosing to be assholes because....er....I don't know why. (Though, I'd be rude too, if I had to live in such an unpleasant place.) Bostonians behind the wheel are a whole other animal - the main hinderance these folks have is they just don't know how to drive. I'm not trying to pick on Boston drivers (I am one), but I can speak from experience that the driving exam in Massachusetts is a paltry excuse for a licensing exam.
New York City Drivers
I am convinced that NYC drivers (at least those that are actually licensed) are completely capable drivers - they must be to deal with driving in that city - they just choose, or are forced due to the stress of living in such cramped conditions, to be jerks. They will cut you off, forget what a "directional" is, and pretend they don't understand rotaries, just to name a few of their inconsideracies. In short, these drivers are controlled, educated maniacs.
Boston Drivers
Bostonians have an unsaid code when it comes to driving: "If I don't see you, you're not there. And I'm only looking straight ahead." This can account for much of the bad driving you will encounter in and around this city. However, the rest of the assholes on the road have an excuse (as flimsy as it is): we in Boston are not taught nor are we required to prove during our license exams that we can do such things as parallel park. Now this is crucial, as most all parking in and around Boston requires you to parallel park at some point if you want to avoid the outrageous fees garages charge. So, instead of even attempting to park correctly, many people just double-park next to another correctly-parked car, or they'll just stop in the middle of the road and put their hazzard lights on (and sometimes not even do that). These people have never been properly trained on how to conduct themselves behind the wheel of a car and they'll be damned if they're going to start learning now! Boston is one city which, in many cases, fears change. The city's old, it's crumbling, and damnit, we like it that way! So don't even try telling a Boston driver that perhaps he or she wants to refresh him or herself on the rules in the Massachusetts Driver's Manual. Trust me. I mentioned it to a crazy bitch this morning who got out of her car at a red light to yell at me for leaning on my horn when she quite obviously cut me off while I was getting off a rotary. She went ballistic. She even told me that if she'd had a gun she'd shoot me. What a pleasant way to start your day.