Years ago, I went on a ski trip with an FWB. We stayed with a friend of his, and the three of us became very well acquainted!
The next day, after skiing, I wanted to shower for the night's activities. My date and our host said they'd invited a few friends over. They told me not to bother dressing after my shower, as it was a very open and informal group!
Of course, I got done and walked totally nude into a roomful of fully- clothed men! I was surprised by how uninhibited I was; once the initial shock wore off, I just went with it and remained naked the rest of the evening!