The name for the character Tina came from Twinkle Khanna who has the same nickname.
During a bike riding sequence in one song, Kajol lost control of the bike and cut her knee quite badly. You can just see her losing control before the camera cuts out the shot. Kajol hit the ground hard and actually lost consciousness for several minutes.
During the first basketball game, we see Shahrukh Khan and Kajol "supposedly" jumping high in the air to shoot a basket. The hoop was actually a bit low, and they used trampolines to jump.
Karan Johar wanted Rani Mukherjee to be dubbed due to her husky voice, not knowing that her voice would become her trademark.
Director Karan Johar never considered his good friend Rani Mukherjee for the role of Tina. In fact, Rani read the script herself and went up to Karan saying, "I'm the only one able to do this role."
The scene at the end of "Ladki Badi Anjaani Hai" where Kajol's sari flies in the air and Shahrukh Khan realizes her love for her, was not originally in the script. Farah Khan added it, believing it added a filmy touch to the scene.