Right now it would be boxers, BUT any of the ones that do not have a problem with the button staying closed. Some of the ones i have, the button won't stay closed, & the little guy takes advantage to always come out & say hi. Though i typically wear boxers every day, i'd be mindful what i would wear THAT day.
Unless i brought along a spare, i would be cautious against wearing white. With my luck, it would wind up getting stained in some form or fashion right before i went in, & that would be embarrassing. Although i did wear white briefs for my first full body scan with the lady dermatologist, but by that time, i had had a few visits with her, so she wasn't "new" new.
Right now, September 19, i would wear boxers to a new doctor. Ask me again after my dermatology appointment in November. Subject to change depending where my mind is at then, i am planning to wear my white 1" McDavid jockstrap to my next full body scan, citing a few spots i've seen on my cheeks, since i'm never asked to remove or lower my boxers during her scans. Yes yes i know full body dermatology exams should be done in the nude anyway, but what can i tell ya?
I haven't had a primary care physician since like forever, due to being healthy, annual physicals at work, & seeing specialists as needed (colonoscopy, orthopedic surgeon, dermatology etc). The plan is to have found a female pcp & have scheduled an appointment not long after my next skin screening. Assuming i go along with my plan & wear my jockstrap for that, barring a bad experience, it will open the door to me wearing jocks more often where i'd be seen, and so i think i would wear a jockstrap then when having that first appointment with my new doctor.
If my dermatologist touches one of the straps or the waistband, given it'll be my 1st time exposed in one AND my intense jockstrap fetish my cock might go flying out of the pouch (as long as i'm not too nervous. & remain shriveled up).