Demanding anything is the best way to piss people off, especially when you demand something from a stranger with nothing in return... Bad idea and kinda jerk move. Yep.
In your specific case it seems that the main issue is with the form rather then the proof of your sex tho.
For example if I came to you and requested the voice chat thing, because my previous eb was a guy pretending to be a girl (my actual eb was bugging me all the time how much she wanted to prove her sex - and I certainly enjoyed the proof :3) which as the result leaves me insecure about said topic, I doubt you would have easy time refusing such request.