One fashion trend that I can think of that changed the world was the invention of the high heel. They were once considered manly because early horse riding was hard to do without a way to keep a heel in the stirrup. The high heel fixed this - usually through the use of an inch high heel on the very back of the shoe.
Then women began to wear them in an effort to look more masculine, and that backfired on them. Now, the heeled shoe has changed in almost every way except one: most heels are still at the very back of the shoe, where they were originally designed to be due to use. Those can barely support weight and make it difficult to wear flat shoes if you wear heels all the time.
I should think the loin cloth! Although would prehistoric man think of this as 'fashion'; more likely, modesty. Let's bring it nearer to you in time and the things that really changed the world culturally tended to be items that people stopped wearing, rather than adopted.
For instance, the bustle, the corset, the burqua are all items that limited freedom. The consquent change in female behaviour was life changing and mind changing for males.