Hey Arnold/Tear Jerker

During Helga's flashback to when she first met Arnold "Dr.Bliss: So nobody ever notices you?
 * Pooter...just Pooter.
 * The ending of "Pigeon Man".
 * The life of Pigeon Man in general is sad. Heck, the original ending was planned to have him jump off the roof before the networks said no to it.
 * Helga's family situation in "Helga on the Couch". Before, people were laughing at her family situation...then during that episode, nobody was laughing anymore.
 * This exchange brought tears to my eyes when I last watched it:

Helga: ...There was someone."

""I can't find my mom and dad.""
 * Lila may be widely disliked, but her situation in her first appearance was heartwrenching.
 * The beginning of Arnold's Christmas where Mr. Hyunh gives up his daughter so she can have a better life.
 * "Parents Day," where Jerkass Big Bob thoughtlessly calls Arnold "orphan-boy" at the family event - sending him into a Heroic BSOD. Later, Arnold asks Phil for the true story about his parents. Lots of fun and heartwarming moments, until the final flashback where baby Arnold says goodbye to his departing parents for what turns out to be the last time. And that dream he has after hearing the story.


 * The episode "Curly's Girl," in which Rhonda repays a debt to Curly by pretending to be his girlfriend for 5 days. She dumps him as soon as they agreed it would be over, and everyone hates Rhonda (even her best friend Nadine) for breaking his heart. To win back her popularity, Rhonda tells Curly to pretend to be his girlfriend again, but then HE dumps HER after hearing her in the bathroom talk about how disgusting she thinks he is (after he forcibly kissed her). As a result, people feel sorry for Rhonda and she's popular again. Then Rhonda goes to Curly's house to thank him (she thinks it was an act), and he's sitting on his front steps with his glasses off (for perhaps the only time ever in the series), eyes wide and full of tears. He didn't look like the little psychotic freak he always is-- instead, he's just a depressed little boy with a shattered heart due to his unrequited love.
 * Any moments during which Bob acts like an actual father to Helga, such as in "Quantity Time," when he looks legitimately hurt after Helga tells him to leave her alone after he took her out for a pony ride because he thought she liked it (and thought she was "Seven... eight?" years old). Also occurred in "Arnold's Thanksgiving," when he can be seen suiting up (vest, helmet and all) like a soldier going to war because he thought Helga (and he didn't mean Olga for once) was missing, and declaring that he wasn't coming back until he found her. After Helga walked in, Bob also expressed his thankfulness for Helga as a daughter, which made Helga smile (which she rarely does in her own house). Rare as they are, these moments are probably made more tearjerker-y by the fact that Bob is usually a neglectful Jerkass of a parent to Helga.
 * Harold was a jerk in Suspended, but after seeing how desparately he wanted to get back into school and how sorry he was and STILL not being let back in is pretty distressing to watch. He even breaks down after all the distress.
 * A meta example as we, the audience, as well as Arnold, Phil, and Pookie will never get to find out what happened to his parents.