Had to be when I was about 10. I've told this story before in other threads, but I woke up one morning covered in hives with my eyes all swollen. Mom called my regular doctor, who sent us over to an allergist. (Back then, doctors made phone consults all the time, even without examining you first.)
Mom and I went to the office. he started checking me out, then told me to remove my pants. Both Mom and I balked, and he said to my mother "Does He have clean underwear on?" Mom got indignant and said "He better." Regardless, the pants came off and he checked everything, genitals included, in front of my mother!
We both were expecting him to just look at the swelling and hives, do some tests and tell me what was up. (It turned out that I am allergic to grass. My Dad was mowing the lawn outside and the window was open.) Neither of us expected him to do a complete physical.
Years latter, I understood that, since he had never seen me before, he wanted to do a "baseline" exam, and also to check the areas covered by clothing for hives.
Now, after years in the Navy as a Corpsman both giving and receiving complete physicals, It takes a lot to embarrass me. Although, once when I was examining a female petty officer for back pain, and the doctor had me do a rectal, I was a bit embarrassed. I had never done a rectal on a female before.