In my case, it was seeing barbarians, tribesmen, early humans, and such in books, movies, TV shows, comics, art, etc. /Conan the Barbarian/, /The Beastmaster/, /Tarzan/, and /The Indian in the Cupboard/ were all big influences among those.

At some point I simulated loincloth flaps by tying two shirts around my waist in front and back. And by my teens I'd made a breechcloth out of worn-out pajama pants; I cut the legs next to the seams and crudely sewed them together end-to-end to make a long-enough cloth, then tied the stringlike seams themselves around my waist as the belt. And dressed thusly, I sometimes played a with a few Lego buildings, imagining being a captive tribesman out of his element (a la /Tarzan in New York/ etc), escaping down the side of a wrecked building after an earthquake had partly knocked it over.

In my 20s, I started buying fabric from a fabric store and to make rather neater loincloths. Some were woven fabric, torn along the weave to make straight edges. But most were/are knit fabric, either cotton lycra or T-shirt material, cut along their subtle ribbing to make neat straight edges. I've gone for walks in my loincloths sometimes (as people from the old Yahoo group can attest), though it's been some years. But mostly they're just what I wear around the house, sometimes with tall socks or old pajama pant leggings when it's not warm enough for bare legs.