The most resilient gender conventions in roleplaying games?

[Felhammer]

You never see men in "bikini mail" armor

And if you have, apologies.

I was DMing a game a few years back where the Dwarven Rogue's player had mentioned wanting to find some kind of special leather armor that would help him be a better rogue. A few weeks later, they were in a necromancer's crypt and came across a create with some discarded armor. The rogue was elated to find the armor he wanted but horrified that it was of the female variety. It had thigh high boots that ended in stiletto heals, a leather thong, a revealing corset-style top and elbow-length gloves. To his credit, the player donned the armor and wore it until the campaign abruptly ended. I think being a Dwarf helped the character, since he had a really long beard to begin with, so from the front, the only thing that would look weird was that he had exposed shoulders and high heels. From the back however... Many a townfolk shot the Dwarf a sideways glance, pondering if he were a female or just a guy with a weird fashion sense (especially considering he never bought pants...)