I think this would be rude and inappropriate no matter who the people involved are. Part of the role of a primary care physician is preventative health maintenance (and if you go to a gynecologist for your routine exam, she is acting as a primary care physician). I am a primary care physician, and generally, I am motivated by the desire to help my patients to improve their health, by whatever means. Yes, my nurse will weigh you every time you come into the office. Yes, I will calculate your BMI. If you like, I can help you with weight management. If you have lost weight since the last visit, I will ask if it was intentional, because unintentional weight loss can be a sign of serious health problems. I have never, in 15 years of medical practice, felt that I have been "put in my place" by a patient losing weight. Usually, I congratulate them, and support them in their efforts. Since I have recently lost weight, people feel that I should share with them how much weight I have lost, what size I currently wear, and what my weight loss goal is. Depending on the situation, and the relationship I have with the person, I may answer tangentially, or not at all. You might get a cold "why do you want to know?", which is how I would respond if I felt a person were asking a question like "what is your BMI?" in a rude and adversarial manner.