I'd have given this a little more negative space on the right and above. I'm not sure centering the 'sensitive part' makes sense. good focus, good choice of B/W
Hmmh. i think this seems a bit unmotivated - kind of like "wooh! We can finally show nipples! I think I will show.... a nipple!". Sorry, but with all the beautiful nudes that exist (both in, but particularly out of this challenge), this doesn't stand a chance.
Lighting is crucial in this kind of photo in order to convey a sense of how you want your viewer to look at the image. As it is, it look more like a technical medical reference shot. Try experimenting with the light source, changing the angles of the light source. 5