A nipple! Will no one think of the children?
No social network will allow the exposed female nip, but they all permit the tit of which it forms an integral part. We don't understand what is obscene or offensive about the humble nipple. Both men and women have them, they define us as mammals, they feed us, and yes — your mother has a couple too. This is not eroticism that is being censored nor the innocence of children that is being preserved.