The majority of things you discuss with your doctor are surely irrelevant to your lifestyle, sore throats, pains here and there...etc.. Doctors, like everyone else, show great variation. Unfortunately the culture within medicine is generally one of conservativism, you would be much less likely to out yourself or discuss issues with your colleagues than other professions.
Although if you look at the 'stats' doctors are just as likely as anyone else to stray into the more perverted areas in their spare time so you may find one who is sympathetic without being able to be openly so. On the good side, any doctor worth their salt will have seen so much shit happen to the human body that a few piercings here and there should illicit little more than curiosity.
Bruising is a little more difficult, there are issues of consent, mental state and cohersion to consider, although as long as you are sane and not a minor this should be a matter of discretion and is usually straight forward.
Serious injury caused during a consenting activity would be a problem, there is legal precedent in the UK of such people being prosecuted, as a doctor you would have a duty to involve social services and/or the police.
If your doctor is really anal about your lifestyle, change doctor, go for the more airy-fairy liberal type than the older conservative.
For interest, the hypocratic oath has not been used universally for some time.