Originally, "About Last Night" was to be made with John Belushi and Dan Aykroyd (The Blues Brothers! No way!), but after John Belushi asked his brother James Belushi, (who had actually starred in the original broadway version) about the role, James Belushi asked that he did not want John to take the part because Jim didn't want to be compared with his brother.
During the scene where they break up at the apartment, the last line Rob Lowe says about not loving her anymore was improvised as Demi was having trouble crying. The line actually reduced her to real tears.
Mother's, the bar that is the central watering hole throughout the film, is actually a downstairs bar in Chicago. They only used the actual front entrance and built a special bar set for the movie that makes it look like its at street level. I visited the actual Mother's on a business trip in 1989.
Demi Moore was in a very serious relationship with Emilio Estevez at the time of filming who was literally best friends with Rob Lowe. An unspoken gentleman's agreement existed between the two guys not to discuss the very intimate love scenes
During the filming of the lovemaking scenes, first-time director Edward Zwick suggested that the crew also take their clothes off to take the pressure off the young actors but Rob Lowe laughed and asked that they didn't because it would be an unwanted distraction!
According to Rob Lowe and Ed Zwick, scenes were shot but subsequently cut where Bernie and Joan got together. Once shot was grabbed immediately after filming the scene by the lake with the balloon showing Bernie and Joan emerging from a car whilst rearranging their clothes.
There are two versions of the movie 'About Last Night'. The regular version we all know and love and a censored version of the movie for TV. Changes in the cut version are as follows: (1) When Dan and Bernie are in their office, they talk and suddenly their boss enters the room. They pretend to be on the phone. In the normal version they give him the finger, in the censored version the make fun of him by putting their thumb against their nose and waving their fingers. (2) While Dan and Debbie make love to Bob Seger's 'Living inside my heart' in the normal version, they throw an American football to each other in the censored version. (3) When Debbie moves out of the appartment she shares with Joan, they seperate the pieces. After Joan asks 'Can Debbie come by on tuesday night', Danny says 'Haha, that's funny, why don't you take this thing and shove it up your a*** in the normal version. In the censored version he says 'Haha, that's funny, why don't you take this thing and shove it up your throat'.