I suspect this was a very real fear for those of us who had to undergo naked examinations involving genital manipulation as teenagers. It certainly happened to me during my first ever examination by a female doctor as a 13 year old Grammar School boy.
I remember my nerves jangling far more than usual on the day itself. Several of my classmates knew I was due to be examined. During morning break two of them told me that it was a woman doctor. They knew because one of them had an older brother, eho had his exam earlier that day. They were teasing me horribly and saying that my cock had better not get stiff or I would be reported and caned.
Stupidly, I believed them. Given the ultra strict censures about anything related to sex ( frowned upon and viewed as filthy, evil, dirty etc).. it naturally preyed upon my fears. I really did feel sick when I was called out of double maths to go for my medical. Whilst the 6th form prefect spoke briefly to the maths master, I waited nervously near the door. One of my friends risked whispering to me: "Just think..pretty soon you will be in the nude with a woman feeling you up.." He stifled a giggle. I just felt sick, genuinely sick.
I knew the routine for medicals very well. I knew I would be naked. I knew that my balls and cock would be checked. It was always mildly embarrassing....but this!! I had never been touched by a female like that. Despite the terrible feelings....I did get semi -hard as she palpated my balls, retracted my foreskin and checked my penis. It was a mixture of acute embarrassment and very real fear.
She must have sensed my unease as my penis was stiffening. I was close to tears. She just quietly asked me if I was alright. I nodded, but then croakily spluttered "Sorry....." She just matter of factly said there was nothing to apologise for and went on about a perfectly normal reaction from a healthy young boy.
Quizzed by my friends later...I desperately tried to play it all down. I did not want them to know that I had begun to get hard. I was still terrified that I might be reported to iur fearsome Headmaster and be caned. I worried about that for about the next 7 -10 school days. Of course, it never happened!!
The only other time I got hard during an exam was 2 years later ( aged 15) when I was examined by a distinctly pervy (but not unpleasant or threatening ) male doctor. By then I knew that I would not be reported for having an erection....but the fact that I was worked up into one did leave me feeling bewildered and confused. I never had an erection in any other exam after that.