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Cagney un der yidisher shprakh
In this matter of knowing Yiddish
Jimmy Cagney had not kissed the Blarney Stone. He was strictly on the level. "My movie star's a good movie star." Here are two examples from Cagney films:
"In the 1932 film "Taxi" a man anxious to get to Ellis Island to meet a recent arrival approaches a cab being driven by Cagney. Man (breathlessly):
"Ikh muz zikh aylen un geyn arunter tsu Elis Aylend!" Cagney (poking his head out the window): "Shvay, Shvayg! Ikh farshtey! Vilst geyn tsu Elis Aylend. Di vayb iz do??" Man: " Vo den! - (With surprise) Bist a yidisher yung!?" Cagney - " Nu vos den - a sheygets!? Khap zikh arayn."
The man quickly enters the taxi.
The second film is "The Fighting 69th"  A group of World War 1 recruits are in formation for inspection and Cagney is standing next to a short Jewish soldier who just finished telling the sergeant that his name is Murphy. Sergeant "Did you say your name is Murphy?" Jewish Soldier: "I did your worship; save in your presence."
Sergeant: "What were you born?"
Soldier: "I was born a boy!" The sergeant walks away in disgust to peals of laughter from the other soldiers.
Cagney (turning to the soldier next to him): " Vos veys er! Er veyst fun gornisht!" Soldier: "Vos veyst er - er iz der balebos!" Cagney: "Nisht far mayn gelt!" While this may come across rather trite in print it is refreshingly cool to watch Cagney as the words come trippingly on the tongue in a glatik, varem, heymish yidish!
Mit vareme grusn,
[taken from a website devoted to questions about Yiddish]
On the other hand, I've kissed and clipped the Blarney Stone many times.