The VERY first time, at least that I remember, I was in the ER about age 14. I had stomach pains and, since my sister had just had her appendix out a month or two before, they brought me in. After the abdominal, he had mom roll me onto my side and bend my knee and he went in. I remember it, but I was so concerned about the belly pain, I didn't even think about it, or the fact my parents were in the cubical, until later. (It was not my appendix, but very bad constipation)
The first I have very clear memory was at sick call about age 19 or 20. I remember it because something happened that hasn't happened before or since. I had pain in my left testicle. The doctor was a Captain (O-6) and was an older man. He did the genital exam and noted the area that hurt. He had me bend over the table, and he told me he was going to do a rectal exam. He gloved and lubed up, then went right for my prostate. I jumped a bit, and he told me to hold still. He felt the who gland, then expressed a drop or two of fluid, which he caught on a slide and examined under a microscope on his desk. (I still had my pants down) After he examined the fluid, he told me I could dress. He knew it wasn't an STD because, although not a virgin, I was not at the time sexually active. He said it was epididymitis (a problem I have had several times since) He prescribed 800mg Motrin and an antibiotic, sent me to bed for the rest of the day, and told me to come back if it didn't get better.
That was the only time a doctor has, intentionally, expressed prostatic fluid from me.