I was 21 when I had my first rectal exam. It came about in a sort of roundabout manner. One night, my girlfriend (and later wife) had been anally fingering me with the usual vim and vigor. Next day I experienced a very sharp burning pain in my anal region. It was internal and since hemorrhoids run in the family, i thought I too had finally succumbed. So I made an appointment with a proctologist and had to wait a few weeks for an opening.
When i came, he asked me the nature of my complaint and i very decidedly told him I was suffering from hemorrhoids. Well, he didn't take me on my word and soon had me on my knees and elbows. He used an instrument I couldn't determine, but which was probably an anoscope or an anal speculum. I was still rather sore and the insertion was not very pleasurable.
After getting dressed again, he took me through his findings. With a rather bored and disapproving face, he drew me a depiction of the anal sphincter and muscles and then drew what he told me was a long cut, lengthwise. As he explained that I had been cut and was not suffering from hemorrhoids I believe that my face turned all shades of red. Because I realized that my girlfriend had cut me internally with a sharp fingernail. I was not suffering from anything else.
The doctor prescribed suppositories and that helped things along afterwards. But as a first rectal exam, it was a bit more embarrassing than usual. It also taught me never to presume to know everything when you are going to the doctors. There are often some embarrassing surprises in store when you least expect them.
Afterwards I didn't tell my girlfriend about the doctor's findings. Mainly because I had been playing the suffering hero for a few weeks and I was getting rave reviews.
But many years later the subject of that exam came up again and I had the pleasure of watching my wife turn just as many shades of embarrassed red as I had done, when I told her what really happened.