"if a guy was sat in a sauna and his balls were on display would you tell him ? would you just look and say nothing ? would you complain ?"
.
At a swingers club or a vanilla setting?
Won't bet an eyelid if it is the former, however, I may have a quiet word if it is the latter, in case the others who are more straight-laced find it unpleasant (it would not bother me the slightest).