Well the most obvious instance that comes to my mind are suicidal persons. I don't think it is legal for someone to say "I am suicidal, I do not want to be treated if I try to harm myself".

I am also not sure of the implications that it entails. If I find someone injured on the street, and he tells me he does not want help, would it then be against the law for me to discard his instructions and help him?

Tuberculosis