Thank you for all those welcomes. JohnJohn is just my screen name because otherwise I'd have to call myself "John9324656735" or something equally elegant.
I think we've got it narrowed down to somewhere between the late '20s (Fitzgerald, Hemingway, et al) and the '60s hippy era. I suspect that it probably fell into (relative) disuse and was then revived in its new incarnation, a bit like "gay".
Continuing on the love theme, does anyone know a phrase "amor fati"? I have no idea where I've come across it, but I have a distinct feeling of "presque vu" (as Yossarian would have it) when I see it written.