I know that the first film is a Hong Kong film, and it is very long, but is the questioner confused? Do you think the girl who pretended to go to the toilet was played by Rosamund Kwan?
Sorry, my previous answer was wrong. The scene you mentioned comes from the movie Bravo, directed by Patrick Leung and starring Carina Lau, Liang Yongqi and Rosamund Kwan. This film was released in 2006 and is a Hong Kong comedy. In the movie, Rosamund Kwan's character underwent sex-change surgery, partnered with his idol, became an actor, and started a funny story about underwear business with Carina Lau and Liang Yongqi. It has nothing to do with what you said about pretending to go to the bathroom blindly. Thank you for your correction.