I have a male massage therapist that I see regularly. Super cool guy, totally straight (as far as I know), and does a great job. I typically keep a pair of underwear on while getting a massage so I can get some passive stretching. Today, instead of my usual Calvin Klein brief or a bikini, I went for a solid black thong. I was SO terrified, and my mind was racing with all the possible outcomes. I pushed through the fear, got onto the table and under the sheet, and just waited.
We're very familiar with each other at this point and isn't quite as obsessive with draping me throughout the massage, so he obviously sees my thong at some point. The massage continued on without comment. He even massaged my glutes (as I typically complain about because of the gym). Afterwards, as I was getting dressed, he actually commented that he preferred when his clients wore thongs.
Huge sigh of relief. We had a little laugh about it. Next hurdle: dating women while wearing thongs.