I don't like the ambiguity of "clothing-optional." I look forward to going to nude spas when in Europe and I have the time. Everyone has a common understanding that it is non-sexual and nakedness is mandatory. It is wonderful being with others of all ages, sizes, and conditions who are naked.
I would definitely go to a vanilla social gathering where I am naked, so long as I know everyone else will be. (It is an interesting thought, however, being invited to a get together where only some of us are randomly chosen to be nude.)
Same if sex is possible; let me know in advance.