Zoro is always shown to compete with Sanji and getting into fights with each other over petty matters, often at inopportune moments. Though they can behave casually and calmly towards each other, Sanji very frequently gets into physical and verbal fights with Zoro.
D: Zoro and Sanji are always fighting! I was reading One Piece and thought it was odd that Zoro never seems to refer Sanji by his name, so I went back and checked! I counted them up from Volume 5 to 66! Here are the results, ranked by frequency!!!
In conclusion, Sanji does in fact refer to Zoro by name, but Zoro does not return the favor! P.N. Little Marron
Oda: “…Okay. Thank you very much, Little Marron! So you counted them all… This was very fun to read! Some of these terms made me wonder when they’d said these things. Indeed, I have trouble imagining Zoro calling him “Sanji” by name. Not once, eh? Wow. Well, they might not get along well, but they’re both valuable, trustworthy men who have Luffy’s back. So let’s forgive them their squabbles (laughs).”