From an interview with Yosef Porat by Yosef "Tommy" Lapid, Ma'ariv, Oct. 19th, 1962, p. 11, brought to our attention by a frequent correspondent:
Botvinnik is very modest and doesn't demand special treatment... Bobby Fischer the American is the exact opposite: incomparably vain, a show-off. Success had gone to his head...
Najdorf lost to Fischer in the  Olympiad. After the game, in which he blundered, I've heard him say: 'I always told myself there's only one chess player I need to fear - Najdorf.'
Nimzowitsch once played in an international tournament against an old English player and got into difficulties. He muttered [in Yiddish]: 'this alter ganef [literally, 'old thief'] tricked me after all...' the English player understood the entire sentence except for the word ganef [thief] but all present didn't want to explain it to him. So finally he asked if a ganef can be a gentleman or not.
The last anecdote was shared by Porat in good faith, but unlike the other two, he was of course not a witness. Is there any proof of the actual occurrence of this 'once' story?
We are skeptical. First, Nimzowitsch is the subject of quite a few such 'once' stories. Second, the opponent and occasion are not specified. Third, we have read at least one other version. In it, Nimzowitsch himself, and not all present, does not want to explain what ganef means. It is added that he quickly agrees that, yes, a ganef can be a gentleman, calming the English player.