This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / The Looney Tunes Show
There is the scene of Bugs letting Taz go back to Tasmania where he belonged. It was saddening to see how these two Looney Tunes characters that bonded together throughout "Devil Dog" had to separate. Fortunately, it becomes happy tears when Bugs finds Taz had snuck on the plane to return to his new friend and master.
Especially when Daffy took all of his money and left him broke. Who didn't want to give him a hug?
Made even worse by the fact that, after all that, he untied Daffy simply because Daffy called him his best friend and said he'd give him a hug. (He lied.) And at the end, it's revealed that Porky donated his kidney to Daffy, and Daffy forces him to help fix the parade float even though he still feels weak from the surgery. Let's hope Petunia makes an appearance soon, because Porky's life could really stand for some improvement.
Petunia finally shows up in what has become a series of episodes where things actually go pretty well for Porky.
Speaking of losers, Daffy was always a bit insecure, but in this series he becomes pathetic to the point of Jerkass Woobie-dom. On his date with Tina, she guesses (correctly) that he cries himself to sleep every night. She then decides that he's not completely hopeless and compares him to a terrible, run-down building that needs to be demolished before it can be rebuilt. Daffy tears up and says, "That's the nicest thing anyone has ever said to me!"
Speedy discovering "Cathy" is Bugs. He plays it off like he was just being nice to an ugly girl, then weeps once he's in his room where we see he was planning to propose.
Oddly enough, "Dear John" gives us a pair of sad moments when Lola and Bugs (individually) think the other has broken up with each other. If anything, it shows that after all this time, they both care about each other, and losing each other is a serious thing for both of them.
In "You've Got Hate Mail", Daffy calling Tina a psychopath turns heartwarming once it's revealed that he just thinks that anyone as wonderful as her would have to be crazy to love him... until you realize what this implies about Daffy's self-esteem.