All the scenes in the diner were filmed last, after the cast got to know each other. The dialogue in those scenes is a combination of scripted and improvisational.
Barry Levinson claims that the infamous football quiz that Eddie forces his fiancée to pass is based on something that one of his male cousins did in real life.
Kevin Bacon had just decided not to renew his contract with the soap opera Guiding Light (1952), and the audition for the film was all he had on the horizon. But on the day he was scheduled for a screentest, he was very ill with the flu and had a fever of 104. It was his intention to read for the part of either Boogie or Billy, but the illness gave him just the right "spaced out, not-all-there aspects of the character," as he later put it, to get him the role of Fenwick.
The greatest source of competition among the actors came about when they were called on to improvise, a skill in which they each had different abilities. Kevin Bacon, by his own admission, was the least adept at it. Tim Daly said it was hardest to top Paul Reiser's improv dexterity because "he's the sharpest, fastest guy alive."
In an interview with TCM years later, Kevin Bacon said that Steve Guttenberg used to eat "incredible amounts of food" and drink milk all the time, and that he looked up to Mickey Rourke as a kind of mentor or teacher. Bacon felt Rourke was very intense and skilled at being "very, very small" in terms of his subtlety, doing work "that you almost are unable to see being shot at the time, and then it gets on-camera and it just, you know, explodes into something great."
Barry Levinson: [Ralph Tabakin] (television customer) has appeared in every Levinson picture from Diner (1982) to Liberty Heights (1999). Levinson, a Baltimore native, is also an Executive Producer, and sometimes director, of Homicide: Life on the Street (1993), where Tabakin had a recurring role.