I actually run into this not infrequently.
For example, I have gotten patients who will accept a sentinel node biopsy but not the axillary clearance, even if their biopsy is positive. As others have noted, I'm not offended nor will I force the patient to have an operation they don't want, BUT in addition to the standard risks, benefits and alternatives statement on the consent form I have them sign a separate consent form. This will state something along the lines of 'I understand that by refusing "procedure x" I am going against the standard of care for my disease and that this decision may hasten and/or cause disease recurrence, spread or my death."
Another example would be the patient who will accept a partial mastectomy for breast cancer but tells me up front that they will not get radiation. Since the risk of recurrence is 39-40%, I tell them I am not comfortable doing an operation with such a high rate of recurrence when it can be lessened by half. Most of the time they come around and I've yet to refuse to do the operation.
BUT...recently, I spent a lot of time with a patient, she chose breast conservation and then at her post-op visit as we were discussing radiation she acts like she's never heard of it. Mind you, not only did I spend considerable time discussing it in the office, I emailed her a copy of my presentation (at her request) which has several slides on RT, CALLED her at home to discuss it further (when I sensed she wouldn't go through with RT) and she agreed to surgery and RT. I have to suspect she manipulated and/or lied to me. So I'm not sure I will agree to BCT again in a patient I think is opposed to RT.
Finally, I've also had patients ask me to do operations which are not indicated - ie, sentinel node biopsy for low grade DCIS, cosmetic procedures. I think as long as they understand the risks and you document them, you're ok...of course, IF doing a low risk procedure.
Patients generally want you to advise them and even guide them. Obviously there are some who come in with their "shopping list" and those can be difficult to handle. The key is to know why they seem to need to control the situation, what it is they really need and want and how you can accomodate them. If doing so makes you feel uncomfortable, then you assist them in finding another surgeon.
What you cannot do is terminate the physician-patient relationship without aiding them in finding another surgeon. Sort of the EMTALA of the OR.