Ain't a DO a bone doctor?

No, a D.O. is a Doctor of Osteopathic Medicine, a type of complete physician just like a Doctor of Medicine (M.D.) Both types of physician attend four years of medical school, residency training, sit for board certification examinations, etc. just like Doctors of Medicine (M.D.). What you are probably thinking of is the difference in medical education between DOs and MDs, which is that Doctors of Osteopathic Medicine, on top of the standard medical curriculum of medical school, receive 300-500 hours of instruction in a form of manual therapy known as osteopathic manipulative medicine (OMM).