The ability to look great while wearing rather atypical things is very close to my personal definition of what makes someone stylish, as opposed to just being well-dressed/elegant. The latter requires some inclination, great patience and a moderate chequebook. The former is impossible for most of us, as it takes a touch of genius/inspiration.
How they do it is beyond me in terms of the underlying mechanics. It's probably a combination of lots of practice (constantly pushing the envelope of what works together & reflecting on successes & failures), a considerable natural sympathy for aesthetics (an eye for proportion, colour, pattern, detail, etc), and a restless imagination. These things feed off each other, incrementally developing the skillset. Having a profession/lifestyle where it's easy to experiment is probably a necessary but not sufficient requirement too. Finally, and this probably goes without saying, but being good-looking (or intriguingly not) also makes a great deal of difference to pulling off good peacock-type outfits.
I would love to be able to work these kind of looks consistently well, but lack at least a couple of the above requirements (I leave it to you to deduce which), so settle for having fun instead. Ah well, there are worse fates. But I do have a sneaking envy for the Tirailleurs, barims, TTOs, Parkers, etc of the world!
PS. I do think it would have been rather nicer to simply hyperlink to the waywrn post of the poor fellow with the unfortunate outfit in the OP rather than embedding the entire post inline for ridicule. It's not a pleasant way to treat another person in my opinion - logically defensible, of course, but still not pleasant - but each to their own I suppose.