It makes me sick that fat people have to deal with this kind of treatment from some some medical professionals (and I say this as a fat person myself). I think that the fact that he would suggest weight loss surgery so nonchalantly is a huge red flag. He might just be unethical, getting kickbacks or mutual referrals from his friend. Or maybe he is prejudiced against fat people. Or perhaps he is just incompetent. In any case, I am glad that you do not plan to go back to him. I would go suggest you go farther and file a complaint against him.
Gastric bypass is not some magic panacea - it is major surgery with potential for serious complications, including death. How he could think it was appropriate to address the topic of your weight in this matter is mind boggling. For all he knew, you could be suffering from an eating disorder or in recovery from one. Or maybe you had an untreated medical condition that contributed to your weight, a condition that perhaps he should be investigating.
And the fact that you were nude, covered only by a sheet, makes it even worse! He had you as his captive audience, and he held a huge amount of power over you.