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Tearjerker: The Breakfast Club
Pretty much the entirety of the scene once the kids have settled down following the scene with the pot; They vary from being at each other's throats to genuinely caring for one another, but what struck me the most was this moment; the compulsive liar◊ of the group basically opens up her heart in the sweetest of ways.
After Allison says, "When you grow up, your heart dies." John, stung but trying to act cool, flippantly asks, "Who cares?" Alison's tearful reply, "I care", gets me every time.
The part where you realise that Allison is absolutely telling the truth when she claims her parents ignore her; Watch the beginning of the film again, and see the scene where her parents just dump her and drive off without so much as a word.
The end of the movie. Lots of romance, lots of happiness and optimism as they leave the school. And the odds are good that as soon as they get to school at 9:00am Monday they'll pretend not to know each other, or at least Andy, Claire and Bender will ignore each other and Brian and Allison.