This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / A Charlie Brown Christmas
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.
Whwn 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.