When did the term "flip flop" displace the term "thong" in North America for a type of sandal?

I grew up in New York (born in Nov 1968) and when I was a child they were called "thongs". In the very late 70s my family moved to Seattle and there they were also called "Thongs". I only became aware of the term "flip-flops" in the late 80s and found it humorous that a g-string would be called a "thong". (I can still recall my adolescent thoughts regarding the idea of comparing butt-cheeks with toes :)

I now live in Germany, so I may be a bit out of touch with some of the current trends.

I find it interesting that "young people" in America today giggle when we "old people" call them "thongs" and they need to "correct" us.

In the 1960s and early 1970s in the New York metropolitan area, people did refer to the shoes as thongs. It was from the early to mid-1970s that the transition to the term "flip-flops" started to take hold, with thong becoming the term for a bikini bottom with minimal covering over the derrière area.

I grew up in Los Angeles in the '80s and we referred to them as thongs. My experience is that flip-flops displaced the word thongs when the underwear became popular in the '90s.

Thong is still used. So is flip flop and sometimes just sandal. We know that.

Thong has been used less because when we hear the word (at least in my part of America) we think underwear not sandals. So I believe the term flip-flop is just more accurate from a marketing point of view. If I am paying big bucks to market my new sandal line, I don't want some of my market base thinking I am pushing underwear. And then through all of the advertising the common term we use changes.