A fellow paisano once commented that there is nothing as bad as a liberal guinea. He was referring to Mario Cuomo at the time but it fits so many.
It’s just that De Niro is only a quarter Italian, at most. The rest of him is mostly Irish. Hence the temper, the verbal abuse, the popping veins in his head and neck.
For centuries, Ireland was “the poor man of Europe”, with a repressive religious culture featuring shaming and corporal punishment, and an oppressive, punitive overlord, England.
While Ireland’s productive class has given the world beautiful literature and amazing agricultural products, the everyday people were for centuries infected with poverty, low self-esteem, rage, and alcohol abuse. Even when those conditions are lifted, the behaviors stay behind until the individual makes an effort to reform.
Instead of reforming his own character, this man became famous projecting all that hatred into portraying criminal characters, sliming the reputation of Italian Americans in the process.