1969, John Kennedy Toole, A Confederacy of Dunces, chapter 2, pages 54 and 109:
He billowed out again in the direction of the music, the shower shoes flapping loudly against the soles of his huge feet.
Mrs. Levy gave the shower shoe a tragic glance.
2011, John Rudolph, A Squid's Story My First Four Years in the United States Navy, Lulu.com (ISBN 9780557169009), page 328:
Goldberg took his leap but his shower shoe came off in mid flight. Distracted from this, he looked back, and that's when he lost his footage on the doorway edge at the entrance, and fell flat down on his bare naked ass into the stale urine. It was too late. He frantically got up but his shower shoe-less foot once again slipped on the deck plate, and this time he rolled directly into it with his clean towel. He was furious since this was his only clean towel but I let him get back into the shower ...
2011, Rod Powers, Basic Training For Dummies, John Wiley & Sons (ISBN 9781118088968), page 127
Shower shoes (flip-flops) are mandatory in basic training. Because a lot of people are living in a confined space, you're not allowed to run around barefoot, spreading your evil germs all over the nice, clean floor. If you don't have shower shoes, you'll be running around the barracks in your underwear and combat boots, which looks sort of silly. Shower shoes are usually readily available at the BX/PX, but why take chances?
2017, Stu Garrard, Words from the Hill: An Invitation to the Unexpected, NavPress (ISBN 9781631465994):
Women come in all the time from the jails, and they don't have shower shoes—and they have to get in a communal shower without shoes, which is not good. I realized that we sold these shower shoes for seventy-nine cents a pair. I could only buy three pairs a time—that was the limit—so I started buying three pairs of shower shoes every week and putting them in a box in my office. When I got fifty pairs bought up, I went to the unit manager and I said, ...