John Belushi's performance in the cafeteria scene was entirely improvised. When he began piling food on his tray, director John Landis urged the camera operator to "stay with him." The infamous "I'm a zit" gag was also improvised, and the reaction from the cast is completely genuine.
DeWayne Jessie's performance as "Otis Day" was so successful that he legally changed his name to Otis Day and subsequently toured and recorded with "Otis Day and the Knights."
Reputedly one of Donald Sutherland's personal favorites of all his films. He described working in it as the funniest experience he had on a set.
Donald Sutherland was so convinced of the movie's lack of potential that, when offered a percent of the gross or a flat fee of $75,000 for his three days' work, he took the upfront payment. Had he taken the gross percentage, he would have been worth an additional $3-4 million.
After firing the crew hairdresser (who wanted extra time off), John Landis took the core Delta actors to a local barber shop and asked the barber if he could do early 1960s-style haircuts. The man looked at the pictures and said it would be easy. He did all of the actors' haircuts, one after another.