Scarlett Johansson: (revealing her fascination with men's nipples) The one thing I don't understand about men is nipples. I don't know if there is one aspect of men that I don't understand other than why they have nipples. Honestly, why? I guess it has something to do with the X chromosome. What is the function of the male nipple? Maybe we all start as androgynous creatures and then they become men?