Obama has fliped the bird, on more than one occasion, sort of. He has extended his middle finger with his other fingers curled, but it is not in an obvious FU gesture. It is a subtle scratch or swipe. Depending on your mood, you can read his repeated action in one of two ways; either the repetition proves it is unconscious or he has to know how people are reading it now and continues to do it anyways. I am leaning toward the first.
Video embedded below.