Rizzo's hickeys were real. Stockard Channing said in an interview that Jeff Conaway insisted on applying them himself.
"Hopelessly Devoted to You" was written and recorded after the movie had wrapped. Dame Olivia Newton-John's contract for Grease stipulated that she should have a solo song. However, nobody had any ideas for a song for her character, Sandy, until Olivia's producer John Farrar came up with "Hopelessly Devoted To You" halfway through the shoot. Director Randal Kleiser wasn't wholly convinced by the song at first and had to come up with an entirely new scene to fit it in. It was eventually filmed and recorded after the movie had wrapped and it earned the film's only Oscar nomination.
In the stage play, the song "Look at Me, I'm Sandra Dee" had a reference to Sal Mineo, who was murdered in 1976. For the movie, the lyric was changed to reference Elvis Presley. Ironically, the slumber party scene in the movie, and the song, was filmed on August 16th, 1977, the day Presley died.
Jeff Conaway was so infatuated with Dame Olivia Newton-John he was tongue-tied whenever she was around. He later married Olivia's sister, Rona Newton-John.
In 2019, Dame Olivia Newton-John auctioned the leather jacket and pants she wore in the finale for $405,700, for the benefit of her cancer research charity. Spanx founder Sara Blakely bought the pants. The anonymous winning bidder of the leather jacket, which sold for $243,200, later returned it to Olivia.
Patricia Birch: The Choreographer, and Director of Grease 2 (1982), is one of the dancers during the contest.
Michael Biehn: When Danny (John Travolta) and Kenickie (Jeff Conaway) put the frog in Patty's (Susan Buckner's) bag. He can also be seen in the scene where Coach Calhoun is trying to show Danny how to play basketball. NOTE: This is not strictly a cameo appearance, which happens after an actor or actress has achieved success. This was simply an uncredited appearance early in Biehn's career, while he was still a struggling actor.