back when i was in high school, my girlfriend used to call me 'puppy' (and i used to call her kitty-kat, baby-tittens, etc even though being a total badass, i didnt care much for these nicknames in public) and no questions ever arose.

frankly you and your master can call each other whatever you want, for whatever reason you want. if someone has a problem with it, you are entitled, as human beings, to tell 'em to go fuck a toaster in the bathtub