Size does not matter to this bee. It is determined to get the much larger hummingbird to leave. When subtlety doesn't work it tries a more direct approach. The video is a clip from the longer video 'Hummingbird vs Bee'.
A pesky bee will not leave the hummingbird alone. The hummingbird sits and preens, takes a moment to scratch his head and beak, trying to rest in the late autumn sunshine nut the bratty bee will not give him any peace.