In general, practical clothing and body armor for when you’re fighting against people who are trying to kill you is not going to have much in common with outfits that make you look hot. For example, on one end of the spectrum you have the chain-mail bikini and on the other you have the US infantry uniform. So what fictional designs yield the best combination of practicality with sexy?
When people are trying to kill you, why should sexy even be part of the equation?
I mean, if one outfit will increase by 2% the chance that I will live to have sex again, I’ll take it even if it decreases my sexiness by 68% while it’s on. You know why? Because “alive” is a fuck of a lot hotter than “dead”.
You aren’t a US serviceperson by any chance? 
Yeah, Battle Babe fantasies are pretty unrealistic, which I conceded in the OP. But that disclaimer aside?
Well, for outright silliness, there are fictional universes where some variation on “narrativium” applies, where story plots and convictions have actual force. In that case a sexy young lady dressing in some fetish outfit made mostly of straps and cords would be highly protected since Sexy Girls don’t get unsightly wounds on exposed flesh. She’d want to wear a helmet or shave her head though since hair can hide injuries.
For a more serious idea, consider force fields and other invisible means of protection. If obvious physical armor is useless but force fields or whatever work, then battle garb could just consist of “don’t wear high heeled shoes”. And if your “force belt” or whatever grants flight, you can keep the shoes.
For something more likely to work in the real world, there’s simply having a combat-rated cyborg body Ghost In The Shell style; you are the armor. Which has the advantage that you are protected at all times.
The there’s Schlock Mercenary “low profile armor”, which looks like ordinary clothing and can be presumably made as sexy as you like short of lots of exposed skin. Proof against most of what we would think of as man portable weapons, granting superhuman strength, flight, and a sealed environment when necessary. And you can wear it all the time, in places where showing up in clomping heavy armor would cause problems.
As for why such a thing as “sexy armor” would be desirable, there are situations where looking good and being protected at the same time would be desirable. Such as being an unobtrusive or nonthreatening bodyguard. Or wandering around in civilian crowds without panicking people. And there’s always formal situations; I can certainly see someone having a “dress uniform” variant. For that matter, our present concentration on plainness and utilitarianism is hardly the only way to do things; some future culture might go back to the days of putting fancy engraving, painting and so forth on weapons & equipment. They might want a sexy set of armor because as far as they are concerned looking good is important.
The current army fatigues are some of the ugliest in history, but it doesn’t have to be that way. I went to high school in the late '70s, and was in Jr. ROTC; one of my classmates was a tall and gorgeous young lady who did some modeling. When she checked out a set of fatigues for some trip we went on – holy crap! (Of course, I suspect they’re supposed to issue them with a looser fit…)
She and I were connected, in a tiny way. When the old sergeant who taught drill was upbraiding our unit for poor posture, he pointed the two of us out as what good posture looks like. And when we graduated, and we were supposed to proceed in boy/girl pairs, her partner punked out, and she asked me to walk with her – possibly for the same reason, or possibly because I was one of the few unpaired males she knew who was tall enough to walk next to her.
In the GURPS role-playing game rules system, there are optional rules for “bulletproof nudity”…just saying.
In RPGs I have run, magic or high tech (see Clarke’s Law), can make very protective armor sexy as hell.
You don’t think it’s intentional? After all, if you’re going to have women serving a military full of under-sexed, macho young men you probably don’t want them looking too hot…
Skin tight leather, yet maximal coverage. Think Trinity in The Matrix, Charlize Theron as Aeon Flux, Scarlett’s Black Widow, Kate Beckinsale in Underworld or the Mord’Sith from Legend of the Seeker.
There was a character in the TOP TEN comic book, Girl 1, who was an android whose skin could change colors & patterns constantly; she was also a “closet” nudist - people assumed she was wearing some kind of bodysuit.
My favorite Alan Moore - I remember her talking about that with IrmaGedden, who was basically a human tank - a pretty funny conversation to be having given the participants…and I think Girl One was a synthezoid/replicant (bio-engineered human/cyborg) vs. an android (human-appearing robot) but I can’t recall…
Yeah, I’m a Top Ten geek…
My definition of a ‘practical’ outfit doesn’t involve having to be sown into it. Then there’s the toilet problem, which I guess you could take care of by providing a groin flap. Not sure that does much for sexiness aspect though…
Not to mention, have you ever tried to move in skintight leather? Plus the squeaking, my god, the squeaking! Practical and leather do not belong in the same sentence.
In terms of actual historical armor, I’d probably go with the whole “Amazon hoplite” look. You’ve got your bare arms and your bare thighs, while at the same time, the breastplate, greaves, helmet and hoplon shield provide perfectly adequate protection.
Well, boots are practical and sexy, even fairly high boots- but not with any significant heel (a modest heel is fine for horseback, however). And, although skintight leather isn’t very practical, leather is fine. Some men find gloves sexy, and of course you’d wear them, and why not high ones?
And a short leather skirt-like garment has been worn by male warriors.
So, let us take a warrioress: thigh high leather boots, a short leather skirt that comes to just about the top of the boots, elbow high gloves, and a cuirboiloi molded breastplate with her boobs & flat tummy enhanced (just like Roman staff officers worn one with enhanced muscles). Sexy, yes- but practical.
A few things that make me wince are bare mid-driffs & super-high heels.
That was pretty much a simulpost, wasn’t it?
Yep. Good one, too!
According to this article, not so much so:
I dunno…actual modern combat garb doesn’t look bad at all, to my eyes. 
If we’re talking fictional, howsa bout something like this?
Roller Derby seems to have dialed in the coefficient pretty well.
Pretty much what I was thinking, with the armour from Mass Effect.