This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Ratatouille
"Gusteau... is dead?"
The subversion of Linguini's attempt of the Rousing Speech, in which Linguini reveals the truth about Remy being the actual cook and trying to rally his crew around that crazy notion. Instead of banding together, everyone decides to up and quit in disgust. The look on Colette's face as she holds herself from delivering a beatdown is especially heartbreaking.
Horst in particular pauses in front of Linguini before everyone starts leaving. The look on his face is disappointment. He was expecting Linguini to be every bit as great as expecting... getting the truth clearly felt like a betrayal to him.
Shortly before, the whole staff moves to kill Remy where he stands without a second thought, and what does he do? He closes his eyes in anticipation. And this is following his I Am What I Am epiphany moment, meaning that he knows that returning to the kitchen will get him killed instantly, but at least he can go out with the comfort of knowing exactly who he is.
What about Linguini? The poor dude, feeling his whole life that he is worthless, never excelling at anything, and never getting respect from anyone, suddenly receives a lot of attention, but more importantly, pressure, of succeeding his Disappeared Dad, two things that he doesn't actually deserve. Then when he comes clean, it's back to square one. Had Django not call the colony to help Rémy cook Ratatouille and Colette come back, Linguini would be left despairing in the chef's office all night, possibly dying of broken heart like his father did.
Anton Ego's climactic speech. It's moments like this where Pixar really shows what it's made of.
All that is good in the world? The stuff dreams are made of?
The chocolate from our childhoods.
The shot at the end of the speech, when Ego refers to him as the "finest chef in France" as Remy watches the sun rise.
The quiet little moment immediately beforehand when Ego tastes the ratatouille and flashes back to his mother's cooking. When you see him for the first time, he's this cold, snide, hard, and impossible to please bougie man. Under all of that though? Buried deep, he was someone who loved food. Someone who once lived to experience, to taste and explore. He had the same fire that Remy has, but after years of criticizing, of making food a job, everything he enjoyed was naught but ashes in his mouth. It took something simple, just a simple peasant dish, something he'd probably not tasted in DECADES, to rekindle his heart. All the fancy glitz in the world couldn't do that.
The ending. Remy is the chef of his own restaurant, La Ratatouille, with Linguini and Colette. Blame the amazing French music.
Ego's grand finale line: Surprise me!, because, man, weren't we all.
Also, Remy mentions how happy Ego is because after losing his job as a critic he became a small-business investor. Ego was the one who used his wealth to help Linguini and Colette with the finances they needed to start their own restaurant just for the sake of being able to continue to eat Remy's cooking and share it with the world. Think about that kind of act from him and how much it says about his love and respect of Remy's talent. It's probably one of the most win-win endings in a film ever! Happy tears.
"Get out of here! You and all your rat buddies! And don't come back or I'll treat you the way restaurants are supposed to treat pests!"
The moment when Linguini lets Remy out of the jar and Remy just runs away. Sure, we know a few seconds later that he comes back, but that moment of sadness for Linguini is pretty terrible. He has to go back and is probably going to get fired again when they all find out that he didn't actually cook it.
An easily forgotten line, but just before the scene above, while gesticulating about what he would do with Rémy, Linguini muses that he "has lost everything" and would salvage anything just to keep himself from being fired from Gusteau's. There are several implications about this as the movie does not detail Linguini's past, but it is likely a gig at Gusteau's is probably Linguini's last chance on sustaining a stable life with a stable income, however small. He might have been fired from all his previous jobs, or worse, never getting one at all (this might explain why he has to slightly bribe Skinner by presenting him with Renata's letter). To say nothing of his run-of-the-mill apartment, or the fact that he has just lost his possibly only living relative. When you think about it, it is a miracle that Rémy come to his life.
The story of Gusteau's death, which suggests that he literally died of a broken heart after Ego's damning review of his restaurant; It especially comes as a major shock as Remy was watching the story of Gusteau's life on television, feeling enormous inspiration from his ideals about cooking.....Only to learn that his beloved icon had been dead the whole time.
Worse is that Gusteau's death was inspired by a real life event: A very beloved and popular chef in France known as Bernard Loiseau (who's past served as inspiration for Gusteau) committed suicide after rumors that his restaurant was going to lose one of it's Michelin Guide stars, which he had built up after years of hard work and ambition. Makes Gusteau's character a lot more depressing.
Not helped that Skinner attempts to make a Gusteau frozen food franchise, which is exactly what happened to Loiseau.