Upon the film's release, the Shirley family stated that Tony and Doc were not friends, they had "an employer-employee relationship". In January 2019, audio recordings of an interview with Don Shirley emerged in which he stated, "I trusted him implicitly... You see... not only was [Tony] my driver, we never had an employer/employee relationship. You don't have time for that bullshit. My life is in this man's hands!... So you've got to be friendly with one another."
The pizza scene is drawn from real life: Nick Vallelonga said Tony Lip used to order a whole, unsliced pizza pie, fold it, and eat it. Upon hearing the anecdote, Viggo Mortensen insisted they try to fit it into the movie. Peter Farrelly protested, saying there were enough funny eating scenes, but agreed to try it. When the crew burst out laughing, he agreed to leave the scene in.
Prior to filming, Viggo Mortensen was invited to meet Nick Vallelonga's family over a six-hour dinner. He said, "It almost destroyed me because I hadn't gained the weight yet - I hadn't expanded my stomach... It was almost lethal..." When the family assumed he was declining more helpings because he didn't like the food, he felt compelled to finish his plate. But every time he finished a plate, they brought another one. "I said goodbye. We did a picture together. I limped to my rental car and I made a big show of 'oh, I'm driving back to Manhattan!' And I drove around the corner, parked the car, leaned my seat back, undid my belt and lay there for an hour, just groaning."
Nick Vallelonga pulled a fast one in hiring his real-life family members to play the onscreen family members. He let Viggo Mortensen believe Peter Farrelly had cast them, but suggested to Farrelly that Viggo had vouched for them as actors. The two only figured out the truth a month into the press tour.
The real Tony Lip is best known for playing Carmine Lupertazzi on The Sopranos (1999) and has had roles in several Martin Scorsese movies.