I have couple surrounding my vasectomy years ago and another that is a little more recent.
The first one was when I went in for my pre procedure counseling. They indicated my wife could come in with me, as the decisions did affect her in some way, too. After the counseling session, the PA - an attractive blonde - had to do an exam. I hang about 5 or 6 inches and have very large balls that can hang in the 7 inch range and I was having a good day on both parts. Anyway, the PA was basically waist high when I pulled off my underwear. Out of nowhere my wife blurted, "he has a big one, doesn't he." Both of them immediately turned red. I ended up with a plump semi as she complete the exam. When we were walking out, I asked my wife why in the hell she did that. She said she was just nervous and she didn't realize the visit was going to include a woman handling my penis and scrotum.
The second was when I went in the for actual procedure. The surgical nurse was a good looking younger woman. I was already shaved and laying with my genitals exposed when she started to prep me. I went from a raging nice flaccid, to a fat semi to a raging hardon in a matter of minutes. She gave me a little bit of a sly look, gave me an injection of anesthetic and covered me with a cloth that was made of the same sort of material as a paper hospital gown. As she was moving the tray of instruments to the other side of the bed the doctor came in. Once he started talking to me I lost the erection and he got on with the procedure. The problem arose when he switched to cut the left side. As soon as he sank the knife into my scrotum I had an incredible searing pain. I actually jumped off the table (and stuck my landing, FWIW). We all realized right away that I had not been numbed on the left side. The girl was hyper apologetic and they shot me up then. It was not quite as effective, but at the least procedure is pretty sort.
The kicker on that story is I saw the girl in a bar a few weeks later and she sent me over a drink.
The last one was last year when I had an in my vas deferens. It hurt pretty bad, so I went to the doctor. The first part of the story is when I went to my GP, who is a man. When I dropped my pants and examined me he said something about my testicles being extremely swollen and enlarged. They were actually in pretty normal condition, to which he responded "Well, they looked enlarged to me."
The story continued when he sent me for ultrasound. When I got there the tech was a decent looking middle aged woman. It turned out she was the sister of one of my students. She told me to undress, lay on the table and place a small towel over my penis, leaving my testicles exposed. The exam, which consisted of rubbing a warm lubricating gel on my nuts and running a sensor back and forth over then for about a half hour also gave me the inevitable erection. As it grew she appeared get a kind of wide eyed look and, in the end, she quickly tugged the towel up to cover the head that was sticking out. That is how the rest of the exam went - her rubbing my balls, me with a raging boner, making small talk. Really, it was probably better than any lap dance I have ever had and my insurance paid for it. Needless to say, I really had to relieve myself badly when I got home.