Well, in the novel, one of the Capone gunmen that Luca captured swallowed the towel that Luca had stuffed in his mouth, which I thought was pretty bad. Then "Maranzano" died with his mouth filled with half-chewed bread--piss-poor manners in my book.
On the other hand, Vito seemed to have splendid manners. He had the good fortune to obtain a rug through the Clemenza Midnight Carpet Service. Then he had the bad fortune to lose his job. He was starving, according to the novel, but "he couldn't eat the rug." That also may have been the origin of his reputation that he was "notoriously straight-laced in matters of sex."