Living in California, I see these things all the time, even during the winter. I have no doubt that they’re just as common everywhere else, at least in warmer months.
But you should NEVER wear flip-flops. They are awful for your feet and legs.
“Flip-flops” get their name from their distinctive sound. As you step forward, your heal comes off the ground and your toes clench, causing them to “flip” up against your heal with a “flop”.
Well it turns out that toe clench caused by flips flops is terrible for your feet, and calves, and knees.
The problem is that clenching your toe engages muscles on the bottom of your feet in an unnatural way. It results in shortening of the plantar fascia on the bottom of your foot, causing plantar fasciitis, short achilles tendons, clad tightness, and knee pain.
But don’t take my word for it. The venerable Kelly Starret has a great video on the dangers of flip-flops. He couches it in terms of athletes (that’s his target audience), but this is true for all humans with sandals:
Did you follow that? Unnatural shortening of tissues = bad news bears.
What to Wear Instead
I’m a HUGE fan of sanuks. They’re basically sandals with a heel. As a result, they look a lot better, and the best part – they don’t mess up your feet.
Going barefoot also has tons of benefits, including the yet-to-be-fully-understood concept of grounding. Even though science doesn’t understand why quite yet, there appear to be benefits of putting bare skin on organic ground (dirt, grass, trees).
Watch your feet get stronger and more stable, and enjoy the decrease in foot and knee pain (and general systemic inflammation).