Nothing to worry about. I usually wear a thong for my waxing session. Like NCThonger said, these people have seen it all. One time, I got waxed by this hot Italian woman and she asked me about my thong tanlines because they were quite vivid. We then talked about going to the beach in a thong. She was a thong girl, and she said she had a couple of thong bikinis at home.
Next time, you should wear a thong to your laser hair treatment appointment. You might have a great conversation with the laser therapist.