I never really saw the fits thing as something being in your size, I saw it as something that fits you specifically, particularly well. And when you find something out in the world that fits it's just lucky coincidence. If all you needed was for something to be your size for the fits bonus, every item in the game would be able to be found or made fitted, and some stuff simply will never fit you. So in my mind we're not talking sizes, although it may just be my own personal bias for how I reasoned things out.
I have rarely tried on clothing of the opposite sex and generally found several minor issues. Particularly in the upper body area. Not that you can't wear the vast majority of it and mostly be reasonably comfortable, but a perfect fit? *shrugs* of course nowadays in the majority of everyday clothes, at least where I live, the only real difference between genders is really the color and design. Shirts and pants for both girls and guys. So yeah, a lot of it is gonna be interchangeable if you want to wear it. And I wasn't really thinking of applying the tags to most things. Mostly just special cases where my head goes "No frakking way this fits completely right"
And when I said skintight suits, I was thinking more on the lines of custom fit near-future tech like wet/drysuits or military spec ops suits. Or certain exercise wear. Not sexy as hell fetish catsuits XD (And while it wasn't comfortable for her think how much worse it would be if one of the set hands hat attempted to try it on) Obviously athletic, water, or mil gear would need to be able to fit you well, and since sizes aren't really present in the game... It just bugs me that you can just put on random clothes from other people and everything in the game will fit you reasonably well, and often exceptionally well.
Although now that they've been mentioned modding in some fetish suits for the lolz and have them be a super rare find in houses might be funny. Or maybe some spandex superhero costumes. Ha. Run around the zombie apocalypse cosplaying as Superman. Some people would probably do it.
On the topic of dresses in the apocalypse. Why would you want all that loose fabric waving around getting caught on stuff constantly or grabbed? Seriously, probably a bad idea. Get yourself a short skirt or some pants or shorts. Preferably pants to protect your legs from scratches or insect bites. And some good solid knee high hiking boots. (Should add some of those to the game too. God I keep thinking of more stuff I want to add.)
EDIT: As for Bra's, yeah pretty much all a guy needs to do to wear one is measure his bandsize. But at the same time he really isn't going to be getting the main benefits of it, given his probable lack of breasts. Hence why I woud gender tag it so he would be getting 0 encumbrance, no harm and little gain, but a she wearing one that fit would be getting a bonus from -1 encumbrance from the support.