Just like the soda/pop controversy, I know different generations and different regions call these ubiquitous summer shoes different names.
I was a kid in the 1960s, growing up along one of the Great Lakes. We, rather predictably, called them beach shoes.
What did you call them in your time and place?
Assuming you mean the cheap foam and rubber sandal things, we always called them flip flops and I’ve never heard them referred to by any other name. Chicago area, born early 70’s.
Zories
Flip flops and/or sandals depending on the exact style and person speaking.
People in my family called them |Zoories| [Kinda rhymes with British “lorries”] and, while nobody else in the neighborhood did so, the knew what we were talking about when we used that term. Maybe it was just sentence context or they were used to us using that term (social context). I figured it was a Japanese term my mother had handed down to us. It’s never been important enough for me to find out where the term really originates.
People in my neighborhood called them “flip-flops” or “thongs” but then the latter term got retasked around the early 1980’s. I figured that was because both were tiny bits of clothing with a little piece that gets wedged between your … toes, yeah, toes, and then comes out and curves around the sides.
My wife learned the Hawaiian term “slippas” while she was living over there.
—G!
60’s Texas we called them thongs. Made things difficult when the underwear came out.
Now I prefer chanclas.
I have a pair of flip flops I wear in the shower at the gym. I refer to that particular pair as shower shoes.
Yup, “flip-flops” or “thongs”.
However, if the retasked version is caught between your toes, you’re either wearing them wrong or having a good time! 
P.S. The ‘repurpose’ is due to global warming.
Flip-flops, or maybe “flippies” or “scuffies” for slang.
Grew up in Michigan in the 60’s.
Called them flip flops.
Learned to call them shower shoes in the Navy.
I just hate it when my thong gets stuck between my toes…makes it soooo hard to walk 
From what the ever-reliable internet tells me, zoris were the original term for the Japanese sandals the south Pacific GIs brought home from WWII, so that’s probably the most authentic name for them.
What we called “shower shoes” in Great Lakes NSTC were completely different from flip flops.
The rubber/plastic ones were flip flops.
Thongs were a step up from flip flops, same style but made of leather.
Sandals were a step up from thongs.
I’m from Hawaii, so it’s slippers (“slippahs”) or zoris to me. My mainland friends have told me that slippers are what you call footwear that you wear indoors, usually the fuzzy ones ones you wear in the evening. But since very few people wear shoes indoors in Hawaii, and it’s too goddamn warm to wear fuzzy ones, that meaning of the word never took hold.
I refer to flip-flops as “the F word” and only call them that when I’m talking to a non-Hawaiian. Kind of like how I know the correct pronunciation of karaoke, but I’ll pronounce it “kah-ree-oh-kee” when not in the presence of Japanese-speaking people.
I would never, ever call them thongs. Thongs, to me, are those strappy footwear things that you might wear for a hike.
Sandals are non-rubber, usually leather, and can be strappier, like the kind of thing you’d wear with a sundress.
What you are showing in your 2nd picture, is what I knew as flip flops as a kid and what we were issued (in white) from the Navy. I did not go to Great Lakes.
(I like the ones you got.)
In Pittsburgh in the 60s we called them flip-flops or thongs. The weird kids down the block called them zories, so we threw crab apples at them.
So did I, although they were beige.
I enlisted in '87, by which time TPTB realized flip flops tend to fall off.
I cringe to remember this but growing up in SoCal, one family I knew called them “jap flaps.” Most people called them “zories” or “thongs.” Never heard them called shower shoes.
Now, I call them “thong sandals” to differentiate them from the other kind of thongs (and other kinds of sandals, for that matter).
I grew up calling them flip flops and called them shower shoes when I was in the Army and I call them flip flops now. Occasionally they might be called thong but not so often.
The military has to have their own nomenclature for everything. A jumping jack is not a jumping jack in the Army, it’s a side straddle hop. I guess “jumping jack” and “flip flop” are too goofy for Uncle Sam.
Well, if the make a “flip flop” sound when you walk, they’re obviously supposed to be called flip flops.
