This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Marley and Me
Jenny's miscarriage. They come home from the doctor's office all somber and subdued and the heretofore rambunctious Marley simply quietly rests his head in Jenny's lap. In the book, John notes this is the first time he has ever not wagged his tail when interacting with either of them. John eventually joins her on the couch and the two of them sit there sobbing as Marley sits there with them.
The end of the book wherein it's described that Marley had to be put to sleep because they couldn't really do anything. This was also made pretty bad in The Movie too. It's probably one of the most triumphant examples of a Tear Jerker in the 20th-21st century because of how close to home it hits, since people are much more likely to experience the death of a pet in their lifespans; even children. Very reminiscent of Old Yeller without shooting the dog.
The Ending montage of Jenny sitting there in the living room, waiting for John to return. The oldest son, Patrick, watching home videos with Marley crying, he really was the only old enough to fully grasp what was happening, and John with Marley at the vet's. The vet assures him before proceeding "He won't feel a thing, he'll just slip away". Marley's eye drift close, and the movie ends with a funeral where Jenny places the necklace that Marley ate at the beginning movie in the grave with Marley, and says "Goodbye, Clearance Puppy"
Carrot Top has on several occasions done a joke where he is on an airplane and they say the in-flight movie is Marley and Me. Carrot Top says "No! not that!" and by the end of the movie, almost the entire plane is in tears.
This is arguably not even so much of a YMMV! Book clubs often avoid this book because it had a tendency to make the readers cry. Schools don't often put it as reading material because students have been known to burst into tears near the end. And in the theatres? Theatre workers have reported seeing a lot of people leave teary-eyed...and these weren't the kids. You could tell who the pet-owners were in the theatre because they were the adults crying.
Perhaps the biggest Tear Jerker is not so much that the dog died, but that it succumbs to freaking hip dysplasia, unable to run, climb stairs, and has difficulty even standing. And yet insists upon following his master from room to room despite this. Watching the wild, energetic dog slowly wind down to a dull-toothed, deaf, and hobbling animal is heart-numbingly sad. Especially poignant was the scene where Marley was struggling up the hill alongside John, and they just sit together, John basically pleading with Marley to tell him when he's ready to pass on because he loves his dog and he doesn't want to see him in pain.
Jenny crying as she hugs Marley one last time and closes the car door and looks through the rear door window. She knows that Marley probably won't be coming back.
In the book, this last part shortly before Marley's passing:
John: "You know all that stuff we've always said about you?" I whispered "What a total pain you are? Don't believe it. Don't believe it for a minute, Marley." He needed to know that, and something more too. There was something I had never told him, that no one ever had. I wanted him to hear it before he went. "Marley," I said, "You are a great dog."