I was entering the rotary from the Arborway. I was on a Vespa. As I was rounding the rotary to head up Center Street, a car sped into the rotary from Cenger Street. Vehicles in the rotary have the right of way of cars who are entering from a street further in the rotary. I had to swerve to avoid him hitting me. He could have killed me. At the next light I stopped next to him and indicated I was going to report him. His response was "go ahead" as if nothing will happen and he didnt care. He was driving a State of Massachusetts vehicle.