There are two types of lefts that qualify as Boston ones. The first is in a T intersection, where a driver is trying to turn left onto a well-traveled (i.e. crowded) road. The only way this can be done in a dense metropolis like Boston of course, is to go halfway and block one lane of traffic. Whether you are the driver or the victim being blocked, remember that you have the right of way.The second type of Boston Left comes at a cross intersection. The situation is otherwise much the same: there is simply too
much traffic to nicely make a left turn. No matter what, there's going to be traffic. So, the only way to complete a left turn is to cut off some sort of artery and block people from moving forward. For definition 2, this means waiting until a green light at the intersection, and flooring it--the driver cuts off traffic that is coming from the opposite direction. This squeezes in a quick turn before people are really moving. One driver pulling a Boston Left is acceptable, two drivers doing this is pushing it, and three means you're justified in getting mad.
