i have a platonic female friend who i go nude with, saunas, sunbathing and sometimes at her flat when i visit. I was going nude before her and until a couple of years she would just going topless at the beach whilst I was nude. First time she went nude with me I got an erection. I felt awkward but she just laughed and said not to worry and soon it went down. Only happened once. You can always cover yourself or turn over.
I agree. Any male will tell u......those things have a mind of their own. Who hasn't had an erection for no reason; no explanation ? Sounds weird and sounds like a lie to those who haven't experience it......but it's true. It really happens. And that, like a woman's monthly visitor, is a fact of life. No shame in it.
The more nude you are the less the erections will be. This will make control easier. Also most all nudist carry a towel to sit on and it can be used to cover up until back to normal. I like to hike nude in the woods and once in a while I will get hard for no reason and just ignore it and it goes away.