"So when the massage therapist is about to massage the..." he points to his rear-end, "what term do they use? Because they don't say ass, right?"
"Yeah, they don't want to use that term." I knew ass was not the right fit, but I was literally stumped. He then asked me what the polite terms were for ass or butt. "Well," I thought. "There's rear."
"But that's the lower back isn't it?" he questioned unconvinced.
"No, you can say rear."
But then I pictured a massage therapist moving down the back declaring, "I'm going to begin to massage your rear." That can't sound right. What about "to massage the rear"? Nope, not that one either.
I propose, "I think gluteus may be the best fit in this situation."
"How about buttocks?"
Now imagine the therapist, as he or she begins to move towards your gluteus maximus, exclaim, "Alright, now I'm going to massage the buttocks"? I think this would be more than cause for laughter, would it not?
So, I told them that probably the therapist should stick with "the gluteus muscles" or "gluteus maximus" or "the gluteus" as it manages to both speak in scientific terms and depersonalizes said under-region of the body. Let's hope it was good advice.