Rav Zeira is called "katina", and we translated it into contemporary English as a form of the nickname "shorty". Although "shorty" may have negative connotations, and "katina" not, isn't this, in any event, a nickname, and something Chazal advised to avoid?
best regards,
Jeff Ram
You are correct that giving nicknames is forbidden, as the Gemara says in Bava Metzia (58b) and as the Shulchan Aruch rules le'Halachah (Choshen Mishpat 228:5). However, this is only when the nickname is derogatory, as you mentioned, or if the subject of the nickname does not like it, even if it is "neutral." Rabbi Kornfeld pointed out that Rav Zeira was called "Katina" as a form of praise; the word "Katina" alludes to humility, as the Gemara in Megilah 10a says, "David was just as humble (Katan) after he became king as he was before."
A further question is the rest of the nickname in the Gemara, "Charich Saki" -- "scorched-legged," because Rav Zeira's legs were discolored (as the Gemara in Bava Metzia 85a, cited in Rashi here, describes). We could answer the same way that we did for the nickname "Katina," that "Charich Saki" indeed is a praise of Rav Zeira, describing his great level of righteousness and faith, that he entered into an oven (l'Shem Shamayim) every day to check himself.
All the best,
Yisroel Shaw