John Hughes was allegedly unhappy with the ending. He wanted Andie to get together with Duckie. But the film's ending of Andie getting together with Blaine was forced upon him by the studio. In retaliation, Hughes virtually made the same film all over again the following year with Some Kind of Wonderful (1987), a film about a similar love triangle. Hughes wanted Molly Ringwald to star in it as well, but she refused. Hughes took it personally, and effectively ended their working relationship. They never worked together again.
There are two bands performing in the club that Andie frequents. One is The Rave-Ups, performing "Rave Up/Shut Up" and the other band is The Talkback, which performs the song "Rudy".
In the scene where Duckie is riding his bike in front of Andie's house while he's mad at her, you notice a red car drive by to the right of the screen, then drive by again in the opposite direction.
When Blaine asks Andie out, directly behind him can be seen a girl in white tights with a blue and yellow dress on. In the next shot, the same girl can be seen behind Andie. Throughout the scene the girl is shown standing behind both Blaine and Andie, even though they are sitting on opposite sides of one another and the view of the playground behind them each is different.
The movie is set in Illinois. After Andie's kiss with Blain, Duckie rides his bike around Andie's house and towards Trax record store; all the cars have Blue California license plates.