I am not a nudist, but everyone I know has seen me naked at least once for various reasons, all non-sexual.
I totally understand Karen showing you her breasts and NOT having it be a moment where she was hitting on you.
I, too, have shown people various things who ask or for various other reasons but not hitting on them. (But being male, I understand that people might say "but that's not the same thing!")
Anyway, the only situation that comes to mind right away is my mother in law. I have seen her naked dozens of times over the years (traveling, sharing hotel rooms, etc), but it's never, ever been sexual. Just casual, and she certainly isn't a nudist. Usually it's just changing clothes quickly, but one time after a shower after swimming she sat in a hotel chair on a towel totally nude for about 20 minutes. She was getting dressed, but she got an alert on Facebook and was distracted by that instead of getting dressed.
She is in her late 60s but could pass for mid-to-late-40s if I told you that was her age, easily. Super perky, real C cups, too.