I like to have a little race on my commute, especially coming home late at night when the young whippersnappers are riding around. But that's a mutually agreed event, nothing like you're describing. If a guy's that rude, just ride at the speed you like and don't worry about him. Say something if it makes you feel better, but it probably won't change the situation. Now if you're feeling fast that day--ask him to race to the end of the next block. Either he'll chicken out or you'll have some fun, win/win.