Nobody Knows Anything - S1-E11
Character mistake: When Tony tells Dr. Melfi he feels as though a safe might fall on his head, she replies, "a feeling of pending doom." A woman of her intellect and education should know the proper word is "impending." "Pending" means something awaiting a conclusion. "Impending" means about to occur.





Answer: It's a mafia thing. Taking food off another made man's plate in public view like that is comparable to the guy in Casino taking off his boots and putting his smelly feet up on the table.
It is not a "mafia" thing, it's basic manners and plain gross for another person to stick their fingers into a plate of your own food. Same with the feet on the gaming table scene in Casino. It's not a "mafia" thing, it's just rude and not something a person does in public.