Reply #2: I have read discussions of this on other web sites,

[begin_within]

particularly gay discussion forums and nudist discussion forums. I won't provide links to them here because they could immediately lead to the display of x-rated images. But if you search far and wide you can find discussions of this. Apparently it was common in the 1950s but it was definitely out of favor by the time I was in high school in the 1970s. Also in the 1950s most YMCAs required men and boys to swim nude, according to what I have read. I still don't really know why though.