While I agree that there are specific times, places and feeling that flipping the bird would be appropriate, I am of the impression that those (like Mrs. Kent) use it because they have the inability to actually use words to put together a point of view that is sale-able. 

In other words, and quoting from a movie here; The first man to raise a fist is the man who's run out of ideas" ~Time After Time (1979) 

If one chooses to be an agent of change, selling out to the lowest common reaction to a event that didn't go your way really does show me that, despite your claim of intelligence, your not that agent of change.