I think this movie is from the 80's. There's a girl who has "I love you" written on her underwear. This guy sees them from a distance. Later in the movie they're in some obligatory chase scene, and she's climbing up a ladder or something and he sees her underwear. Him: "I love you" Her: "I love you too" Him: "No, your underwear" Her: "You love my underwear?" I can't think of the title. It was not a memorable film except for this.