I'm rather new here and just posted this in the thread about hostels. Being new to the site, I'm not sure if cross-posting is frowned upon so please let me know if it is. It just seemed relevant here as well...
Decades ago, after my first year of college, I was backpacking around Europe. One of many memorable experiences was duringt a week at a hostel in Barcelona. My first night there I thought I'd shower so I grabbed my stuff and headed to the bathroom. There were benches in the center of the shower room with curtained individual stalls around the perimeter. I stripped down, left my clothes and towel on a bench, hopped in and had a refreshing shower. When I turned the water off I heard conversation -- with female voices which seemed odd.
I peeked past my curtain and saw two naked women ready for their showers. At first I thought I had just gone to the wrong bathroom, then saw another guy come in. I discovered it was a coed bathroom. I didn't even know such a thing existed!
Being 19 in such an unexpected situation, the realization that I was in mixed company got me rock hard. I was so obviously excited but a bit panicked. My clothes and towel were 15 feet away on a bench in the middle of the room, but I was as erect as I'd ever been. I turned the water back on cold, jerked off and waited for my penis to calm down. I then took a deep breath, got out pretending I'd done this before and toweled off with everyone else (there were both men and women naked in the room then).
In the end it was great for me to have this unplanned experience being nude in mixed anonymous company. Years, when studying at a European university, I wasn't phased to find the bathrooms on the classroom hall were coed. My femal classmates would walk past as we guys were at the urinals. At another point in my life, I lived somewhere with coed natural hot springs. I was totally comfortable and fully enjoyed the mixed company with no anxiety (though I still had the occasional physical reaction which I would keep discrete.) I was raised in a modest, but not repressive family so this was not the norm I knew, but quickly I realized how natural it was.