As a kid, I wore white briefs because that's what my mom bought me. I wore white briefs until going to college and seeing what my hot college roommate wore -- bikini briefs (no joking).
I got some of those, but never wore them to an exam. I had a physical toward the end of my freshman year in college, and I took out the white briefs for those. The small clinic was near a medical school, and the very young doctor was nervous and so was I. He stayed in the room while I disrobed bit by bit as the exam progressed, till I was wearing nothing but the white briefs. He slid them to my knees. My penis was shriveled but I remember my balls were hanging nicely. I was about to turn 19.
I switched to boxers sometime after college. But when I had a physical when I was 24, for some reason I brought out the white briefs. The medical assistant made me strip to the briefs and have a seat on the exam table to wait for the doctor.
I can't recall what I wore to my next physical a few years later. By my 30s, I wore boxer briefs or occasionally sports briefs ... but it didn't matter because the clinics I went to through my early 50s made me strip all the way and put on a gown. I made sure to place my underwear on top of my clothes, so the doctor would see that I followed directions when he entered the room.
There was one exception to that, during a physical I have written about before. For my physical with my second DRE, I could tell the doctor was somewhat into me. He met me in the exam room completely dressed and did not step out after he told me to get undressed. He watched me get undressed. I distinctly remember wearing fairly tight-fitting black boxer-briefs. I recall standing in front of him and contemplating whether I should slide them off, or at least ask whether they needed to come off. But I just had a seat on the exam table in my black boxer-briefs. I wish I would've just taken them all the way off, because my previous physical with him had me naked under the gown.
Had one more physical with him, when I was stripped and wore only a gown. Then he retired. Damn.