SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh. Literal translation: He's an expert like a goat's an expert on a musician. The Yiddish word klezmer refers to the musician, not the music. Variations:
Er iz a meyvn vi a khazer af heyvn. | .ער איז אַ מבֿין ווי אַ חזיר אויף הייוון
He's an expert like a pig's an expert on yeast.
SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten
Er iz a meyvn vi a kats af heyvn. | .ער איז אַ מבֿין ווי אַ קאַץ אויף הייוון
He's an expert like a cat's an expert on yeast.
SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh