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From my all-time favorite movie Pretty Woman, when they're on their way to the opera....
Vivienne says to Edward, "If I forget to tell you later, I had a really nice time tonight." The look of utter surprise on his face is perfect, and then when the elevator operator smiles... Love it. I wish I'd written that. I've seen it a hundred times and it still gets me.
From my second-favorite movie, The Sound of Music, the scene where Georg is breaking up with the Baroness... When she says "Somewhere out there is a woman who's never going to be a nun." Again, the expression on his face says it all.
Tapping into the Julia Roberts library once again, this time from Notting Hill...
"I'm just a girl, standing before a boy, asking him to love her." Sigh...
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I'll add other examples when I discover them! What are some of your favorite lines?