Luigi often treats his customers rudely, insulting and belittling them; at times under his breath, at other times in a conversational tone, and sometimes shouting the slurs to the (unseen) chef Salvatore. Luigi seems to have some connections to the mafia. Local gangster Fat Tony is a frequent customer at his restaurant, despite the fact that he was one of the targets of Fat Tony's plan to get rid of all other food retailers except Marge's. He says the phrase, "I guarantee" a lot.
Luigi may have been an illegal immigrant because he disappeared during an immigration officer's introduction at Luigi's restaurant and took the citizenship exam with Apu.
When Homer was a food critic, he gave Luigi's eatery a poor review; in retaliation, Luigi hired a friend to place a horse's head in Homer's bed (a reference to The Godfather). Homer subsequently ate the head and gave it a bad review.
Fat Tony had Luigi on his list of people he should not shoot.
Luigi can't speak Italian but fractured English as it's what his parents spoke at home. When he ordered cheese for his lasagna he took help from Milhouse with the translation.
Because he is a member of the Hollywood Foreign Press he was selected to tell Bart that Angry Dad was nominated to a Golden Globe.