This is not an easy question for me to answer. Of course, we know you are supposed to report the dog no matter what. I understand logically all the reasons why this is a good thing. However, my honest answer would be "It depends on the circumstances." How serious is in the injury? What caused the dog to bite you? Is this a vicious dog trained to bite people? (If so, why are you hanging out with a friend like this in the first place?)
What would you do?