It used to embarrass me, but these days I always get out of the spa/hot tub with an erection and at the beach I don't worry about covering it up. I don't play with it in public though.
I remember my first time being embarrassed by mine until I realized nobody cared. Then it was all over.
I get partial erections quite frequently in the gym. I consider the locker room scenery to be my reward for working out. I enjoy the variety of the penises in the locker room, steam room and hot tub...... Shaved, not shaved, cut, uncut, pierced, tattooed, etc...... All of them fascinating and generally stimulating. I love to look and be looked at. I don't stroke myself in public, but I certainly don't mind being erect.
It is an interesting phenomenon that we enjoy both seeing and being seen. The fact that another gets an erection in response to seeing one is the most honest of compliments. Nonverbal communication is so intriguing.
It doesnt bother me. Its natural to get erect. If Im erect in a public sauna, locker room or spa I just let it be.
When I get an erection in a setting such as you mentioned I recognize my body is paying a compliment to whomever I happened to observe.