It was an age when it was still permissible to poke fun at ethnic foibles. No one did this better than Fred Allen, through his cast of characters on “Allen’s Alley.” In that skit Allen, as the master of ceremonies, would venture down the alley and knock on the door of its residents: Senator Claghorn was a blowhard Southern politician; Mrs. Nussbaum was a tart Jewish skeptic with a heavy Yiddish accent; Titus Moody was a New England Yankee skinflint; and Ajax Cassidy was a professional Irishman.