I have masturbated after my physicals many times. Two I remember pretty vividly:
The first one was when I was a freshman in college and a few weeks from my 19th birthday. I needed a physical for my summer job as a camp counselor. I went to a clinic where a lot of college students went. The doctor was almost certainly a medical resident – seemed very young to me, even at the time. Pretty sure he was Asian. He was nervous and I was nervous. I recall wearing a pair of loose-fitting stone-washed jeans and white briefs. He had me strip bit by bit until I was in only my briefs. I hadn't been in only my briefs at the doctor since I was a pretty young boy at the pediatrician.
I recall standing in front of him on the stool and the awkwardness of what came next. He tugged at the sides of my underwear and I got the message. I lowered them just a bit but he wanted them lower so he pushed them toward my knees. I recall my testicles were hanging loosely and my penis was quite shriveled from the nerves. I was very embarrassed by how small I was. I got the sense I was one of his first genital exams ever.
After the physical, I rushed back to my dorm room and knew my roommate was at class. It was a short walk, only about three blocks. I relieved the experience in my dorm room. I recall taking off my jeans and getting down to my underwear. I lowered my briefs and my balls were still hanging nicely. My penis was still flaccid but not shriveled. I imagined the view the doctor had and then touched my balls, realizing the last person who had touched them was the young doctor. It was so hot, examining myself maybe 15 minutes after the doctor had done so.
I don't recall the actual orgasm, but I'm sure it was great. I almost certainly was lying down, fantasizing about the whole experience. For several years afterward, that experience formed the basis of a lot of masturbation fantasies.
The second time was after I had received my first rectal exam. I was only 33. It was the first physical I had had in probably six or seven years. When I made the appointment, I disclosed a history of prostate cancer in my family and made it clear that was the main reason for the office visit. The visit did not disappoint. I was naked under a gown for the first time, and had a 60-something doctor's finger up my butt for the first time. He was thorough and not gentle. He wiped my anus afterward, and not very thoroughly.
After it was over, I felt squishy-ness between my butt cheeks as I headed from the clinic and down six flights in an elevator. In the lobby, there was a restroom. I couldn't stand it – I went into the restroom and jerked off as soon as I can, before the lubricant had a chance to dry. Then I went home and jerked off a second time. So hot.