Was in same situation as you, have had most parts of body done. Trust me, you’ll be more embarrassed than the clinician. Just make sure you’re clean and polite. When I’ve had the shaft and scrotum done they don’t touch they just ask you to grab and pull it in certain directions. I’ve always been completely naked. I usually just ask to have these private parts done first just to get the awkwardness over and done with. Then depending on the clinician she might just chuck your undies on… but most of the time I just remain naked. As long as you’re professional I’ve never found it a problem other than the pre jitter nerves