All right...

The answer is easy, it's the same as: would you wear a chainmail jockstrap.

Maybe they're both equivalent, and the character in question thinks the bikini is more comfortable, or that part of their character is to try and look sexy while they kill people. Armor throughout the ages has contained decorations that dramatically reduce its effectiveness just because people thought it looked better, it's even well possible that some people who preferred the chainmail bikini look would compromise their defense for their look. Though an optimizing player would pretty much always pick the full plate, so long as it was actually superior and not merely equivalent.

to get my sweat dick hard

Once again GURPS has you covered.

If I wasn't me and was a rugged, muscled, good looking fantasy character, sure.

If we're going that route women would most likely not even be on the battlefield in the first place, so why bother with armor at all?

fpbp

>Once again GURPS adds extra unnecessary rules to a thing that didn't need them

You would be able to answer this question yourself if you ever spent any time around women

Because they find it appealing or wish to convey something in appearance, combined with the fact that they live in a setting where, for whatever reason, doing so does not significantly decrease their chances of survival.