This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / A Charlie Brown Christmas
I Killed It!
The scene where the kids verbally tear Charlie Brown to bits for choosing the wrong tree, before walking away, laughing hysterically. The scene was mercifully shortened when aired on CBS, making it easier to watch.
Then watching Charlie Brown walk away, completely unfazed by their mockery for once in his life, going home fully prepared to decorate the tree... and immediately "killing" it. The sad frustration in his voice is heart-rending.
When Charlie Brown first arrives to direct the play, everyone applauds him, except for someone making a "booooooooooooooooooo" noise. It turns out to be Snoopy, the revelation of which causes Charlie Brown to say, "Man's Best Friend". One wonders why Charlie Brown hasn't committed suicide when even his own dog hates him.
To be fair, his dog doesn't hate him, he just seems to antagonize him quite a bit, but still.
Charlie Brown's depression is hard to watch, especially today, when we know more about holiday depression and how serious it can be. It's worse if you've actually struggled with depression and know firsthand what Charlie Brown's talking about. It's Christmas, everyone's having a lovely time, there are presents and snow and lights — by all accounts, he should be happy. But he's not. It's especially sad to think about how isolating depression can feel, especially around the holidays, when it seems like everyone else is happy and having fun. And Charlie Brown is, what? Eight years old at the most? Poor kid.