Rectal exam. :(
Mine was a disturbing incidence with a rude OBGYN when I was 38 weeks pregnant with my 2nd child. 😡😤
Bungling my hernia operation and had to do it twice in two days.
I've thankfully never had a bad experience with a doctor. I've had some things done that weren't particularly pleasant (I was born with Hirschsprung's disease, which is a deformation of the large intestine that has caused a number of issues, mostly when I was little), but my doctors have all been very good. I'm not all that comfortable being in hospitals, but the people I see have always made visits as relaxing as possible.
Most of you know my daughter has Down Syndrome. Our doctor didn't make it to her birth, so a nurse and my husband delivered her. But that's not the horrible experience. A doctor we had never met before came in to tend to me after the birth, dragged my husband into the hall, and said "I don't like the look of that baby's face .... I think she's retarded!" (When I finally found out, I filed a complaint and got him fired, at least from that hospital.)