There is a quote about fools that I have heard, which is attributed to the Talmud. It goes as follows, "Never tell a fool he is a fool. All you'll have is an angry fool." I know that there are a number of Talmudic statements about fools. I've asked a number of people if they have ever heard of or read this quote. No one that I have asked recalls this statement in the Talmud. I wonder if it is a Yiddish saying, or if it has roots in some Jewish text, or if it isn't of Jewish origin at all.
A possible source is Proverbs (9:8)
אַל תּוֹכַח לֵץ פֶּן יִשְׂנָאֶךָּ הוֹכַח לְחָכָם וְיֶאֱהָבֶךָּ
"Criticize not the scoffer lest he hate you; criticize the wise and he will love you."
Another close one (26:4)
אַל תַּעַן כְּסִיל כְּאִוַּלְתּוֹ פֶּן תִּשְׁוֶה לּוֹ גַם אָתָּה
"Answer not the fool with his foolishness lest you too resemble him."