(a) This is the only case in which such a name is mentioned in Chazal, as far as I can tell. Alfasi (in Chikrei Eretz Yisrael) calls him "one of the Chachmai Teveryah...". Rav Yosef Chaim (Sefer Benayahu on Shabbos) also suggests that he was a Chacham and Nazuf was the family name, since Chazal certainly would not give a derogatory title to a person who hosted Raban Gamliel.

(b) However, it would seem that the title 'Rebbi' (Yochanan), which appears in the version of the story in Tosefta Shabbos 14:2, is almost certainly a printers' error, and Yochanan was not a Chacham (as Tevor Ha'Aretz, on Teveryah, writes).

As for what Raban Gamliel was doing "at his Shulchan", Alei Tamar (Tel Aviv 1982, on Yevamos 102a) suggests that Yochanan was a moneychanger, or Shulchani (as in Tosfos there DH v'Al Shulchani).

(c) Avraham Orenstein (Encyclopedia l'Toarei Kavod b'Yisrael, Tel Aviv 1964, Erech Nazuf), who raises your question, doesn't find an adequate answer as to Yochanan's identity and why Chazal looked down on him. He suggests that perhaps Yochanan was a translator of Jewish texts, and the Chachamim gave him the derogatory title because they looked down on him for spending his time translating instead of learning.

Alei Tamar (in Shabbos) suggests that he belonged to a group of Chachamim who called themselves 'Nezufim' because they conducted themselves as though Klal Yisrael was put in Niduy by HKB'H, following the destruction of the second Temple. (See Bava Basra 60a, which mentions that there were people who stopped eating meat and wine after the Churban).

(d) Based on context and chronology, it would seem to me that Yochanan was a Talmid of Yeshu Notzri - which is why he is called "ha'Nazuf", or more accurately "Ben ha'Nazuf" (=student of the censured one) as it appears in the Tosefta and Rabeinu Chananel. (Yochanan is generally rendered in English as 'John'. He might have called himself 'Nizeh' in Hebrew, which Chachamim changed to the Nazuf or Nizof to disgrace him.)

In the continuation of the Sugya of Gemara, we find a story about books that Minim (= students of Yeshu) used for staging debates with Jews, and about other Sifrei Minim (116a). The uncensored version of the Gemara there refers openly to the tomes of the Evangelae and the derogatory nicknames given to them by Chazal.)

Be well,

Rabbi Mordecai Kornfeld

Kollel Iyun Hadaf