I’ve had plenty of physical exams by male doctors with no issue. A few months ago I had a testicular ultrasound. The female tech set it up so only my balls were out in the open, while my penis was covered by a towel, but I imagine she had to have noticed the lump under the towel grew a good bit.
Just today I was at the gym. My gym has communal showers. This is only the second time this has happened to me in a communal shower. For some reason, I started to pop a boner. There was one other guy in there, quite a bit older than I, and I did not want him to see. I continued to shower as usual and hoped he wasn’t looking. Once it got to the point where it was obviously more than a semi/chubby, I turned to the side and tried to ‘will’ it down, but it just continued to grow and grow. I realized that it was probably odd that I was just staring at the wall not doing anything after about a minute of that, so I turned off my shower, without even soaping up at that point, grabbed my towel, and went and sat on the toilet until it went down. It took forever. After that, I went back to the shower and proceeded as normal, almost completely flaccid. The other guy was getting dressed at that point. I don’t know if he noticed anything.