Usually I do or say nothing, and neither do they. However I have noticed that they often smile in a way they would not normally, a smile of recognition perhaps, but no more. Occasionally someone says something. Once my PCP said "Good." That was all. She looked at my erect penis and said "Good." I took it to mean she thought it a sign of health (and definitely not a comment about its size, shape or her enjoyment at seeing it!). But otherwise nothing -- no jokes, or wise comments, setting at ease, etc. -- except perhaps a jolt of surprise when they see it (I recall a nurse called in by my female dermatologist to assist in a scraping; when she entered she found me nude and partially erect and did a double take, but otherwise she did or said nothing.)
But two exceptions come to mind. Elsewhere I have written that one of the things I really like about my PCP is her forthrightness and interest in some aspects of my health that not all doctors pay attention to, including my sex life. She asks about my sexual frequency, practices, satisfaction, problems, pain, etc. She has asked me about my sexual history too. The first time she did this was the lengthiest, and she did it during my second or third annual physical with her. I had an erection as I sat on the exam table talking to her and several times she looked at it as we talked, nodding in its direction once or twice as she spoke. I wondered later if the fact that I had an erection had triggered the questions, or caused her to remember to bring up the subject.
The other exception is a bit funny. It occurred during the time when I was being examined for a strange rash on the glans of my penis, the episode I referred to in my first post in this thread. I am not circumcised and the rash occurred at the coronal ridge, underneath my foreskin. So I had to peel it all the way back to show them. With an erection it was of course easy to keep it peeled back, but when the exam was over and they were debriefing me about their findings, I wanted to put my foreskin back covering the glans. For a person like me who is natural a peeled-back foreskin is a bit uncomfortable. But when you have an erection it can be difficult to get it to go over the swollen glans and back into position. Often the foreskin sort of curls under itself and becomes even more uncomfortable.
That is what happened to me when they were through examining me. But there is a way to deal with that situation, a technique I had mastered many years before -- I grasp the foreskin between forefinger and thumb and curl it outwards in several places around the perimeter of the glans, finally stretching the skin tightly towards the end of my penis. The stretching has to be done several times usually. And that is what I was doing, somewhat absent-mindedly, during the debriefing. As you can see, it is a somewhat complicated and unusual procedure and it takes a minute or two to get it done. The first time I did it, I noticed the doctor watching me intently. I realized how fascinated she was by the procedure when she stopped talking in mid sentence and just watched me. I think she was not sure at first what I was doing, and later found it interesting. Perhaps she saw mainly men who were cut and who therefore had no need to reposition their foreskins over an engorged glans. In any case when she caught herself she startled. And then, realizing what she was doing, giggled. I did too. Then we went back to talking. Later the NP came in and redid the exam, and this time when she was done I enjoyed a bit of mischief by repositioning my foreskin with exaggerated precision, and even slower speed. She stopped in mid sentence, just like the doctor, and followed my every move with her eyes. I extended the procedure for as long as I dared and after stretching out my foreskin fully, allowed it to snap back into position with an audible pop. Then I smiled. She laughed. True story.