Hypocritical Private Part nicknames Girls only.?

Ok I have noticed that each of my girlfriends for the past 2 years have called my penis a dick or cock. I do think its sexy but when I call my girlfriends vagina a ''pussy'' she looks at me like I called a black person the N word. I mean I know girls like to be classy and all but it seems hypocritical. Any help? Please no negative comments.