Recently I stumbled across a lot of posts here on DA concerned with drawing the human form, and how to differentiate easily between the male and female form without drawing upon obvious sexual characteristics. It's aaaalll about the skeletal structure.
Basically, as a rule of thumb, the skeleton of a man has wider shoulders than hips, in a "V" shape. The skeleton of a woman has wider hips than shoulders, though not quite as drastically so as the opposite in men. More like an "8" shape. To confuse matters, make them both the same width for an androgynous looking thing. It's simple and it works. As a rule of thumb.
By sticking to this, you can get away without ginormous boobies on your Fe-MOCs, and having... idk, hair or somethin' on a He-MOC.
The post in question is this: by . I really, really reccomend looking up some of her posts concerning proportions and body types. Even though they're geared towards drawing, they also apply to 3D models and MOC making - perhaps even moreso, as quite often with us there's a real skeleton to build instead of an inferred or imagined one.