My brother, who was born male, has elbows that "out-bend", and so do mine. For us, it's just genetic. I don't know about the theory of it being only in women. I think it's just rare in general. Then again, I don't entirely understand the term "out-bend"; if my brother and I hold our arms forwards, palms facing upwards, we seem double-jointed in that we can stretch the arm out to the side, and thus the elbow. Not entirely sure what else it could be, other than the theory that, in female skeletons, the elbows bend outwards to accommodate the hips. This, I do not have.
On the subject of the uncomfortable way of sitting, I do often cross my legs at the knee. I don't know why a comfortable sitting position should ever be gendered. You sit as you want to sit. I've seen many cisgendered males sitting in this manner, and I've also seen them standing and leaning in awkward positions that would be labeled "effeminate". We as people should do what we think is comfortable whether it be branded female or male. And the double leg crossing is simply mind-bending for me.
