Humuhumunukunukuapua'a or Humuhumu, a triggerfish:

The images above are all of the same Humuhumu. It was showing a territorial claim to a specific sand pit and chasing other fish away including larger Humuhumu's. As I would swim in close, it would dart directly at my camera and then flash off and away. You can see that it also was changing its colors as it went about doing "its thing".