I wouldn't be offended, but I get embarrassed when it happens to me. When I was young I was so turned on by being naked in front of other guys that I couldn't use gang showers without getting a raging erection. I gradually learned to control it by gradually increasing the amount of time naked and distance from an available towel. When it would happen, I'd turn the water cold and turn toward the wall. I've generally learned to control it, but I still find it exhilarating to be naked and still have to fight off semis at times, particularly when I'm aware that an attractive guy is looking at my penis