Hiccup's breakdown at the end of How to Cheat a Dragon's Curse might count. The boy has just spent the whole book getting run through the wringer as he tries to get an antidote (a potato) for his dying best friend. Then, just as he is nearing home, a sea dragon breaks the ice and steals it. The others are cheering Hiccup for being The Chosen One who would get rid of the dragon. Hiccup has this reaction:
"I don't want to be chief of the Hairy Hooligan tribe! I didn't want to lift Norbert's stupid curse! I wanted to cheat the curse on Fishlegs! All I want is my friend..."
"All I want is my friend. Fishlegs trusted me. He thought I would make everything alright."
The tears only work up harder when it turns out Hiccup actually has the disease, and there is no potato in sight. Stoick is all but ready to charge out to sea and wrestle the potato from the Doomfang, and Old Wrinkly has to tell Stoick that it's IMPOSSIBLE to seek a cure, after saying that things are IMPROBABLE in the books. Stoick may not be the brightest Viking, but he loves his son.
Hiccup Horrendous Haddock II's story, as revealed in How to Break a Dragon's Heart: abandoned for being a runt, captured by his father Grimbeard the Ghastly when he and his dragon-brother Furious are discovered, forced to witness a world of human and dragon slaves that his father created. When he tries to have the dragons demonstrate peacefully for his freedom, his father kills him, thinking it's an act of rebellion. Grimbeard realizes too late that the real traitor was his other son Thugheart, and Hiccup II dies in his arms. This tragedy is a Cynicism Catalyst for Furious, who vows to wipe out all humans once freed from his chains in How to Break a Dragon's Heart, and a Heel Realization and Despair Event Horizon for Grimbeard. Becomes Fridge Horror when you learn that Grimbeard had the power to free all dragon slaves and become a better king with the Dragon Jewel, but he just chose to ride off into sea after dismantling his kingdom and exiling Thugheart; the whole book series could've been avoided if Grimbeard had taken responsibility for enslaving dragons and humans. In addition, you never hear how Grimbeard's surviving son Chucklehead handled the Trauma Conga Line after witnessing his family kill each other and then made the heir of boggy Berk by default.
Hiccup's situation in How to Seize a Dragon's Jewel; having spent so long isolated from human contact (or when there was human contact, they were trying to kill him) with only a small group of dragons for company, he's almost forgotten how to even speak Norse. Then his mother tries to kill him, and the story starts.
Valhallarama becomes an Iron Woobie in How to Betray a Dragon's Hero, after the witch and Alvin have "proof" that Hiccup has died and imply that Valhallarama's neglectful parenting was to blame. Valhallarama, unable to do any fighting on the Island on Tomorrow, then reveals that she has hoped to repair her relationship with Hiccup, since her fruitless quest kept her away from home for so long, once she got him crowned king. Makes one wonder how she felt when Hiccup yelled at her in the previous book for never being home and for appearing to betray him. Slightly softened in that How to Twist a Dragon's Tale previously revealed that Valhallarama had a good relationship with Hiccup up to the day of her death, meaning they they reconciled at some point.
Elderly Hiccup's epilogues at the end of every book are always poignant, but bittersweet and sad at the same time.
Hiccup, Camicazi and the escape artists helping Eggingarde to escape in 'How to Betray a Dragon's Hero' and her subsequent reunion with Bear Mama. The readers aren't told anymore of what happens after the escape artists leave with her, but the little illustration of her smiling with her mother is enough to make any person smile/tear up a little.
The Windwalker looks positively devastated when he realizes he cannot come with Hiccup, Toothless and the Wodensfang into Fort Sinister because he's too big.
Toothless' first scene.
How about when Hiccup came back from the scene where he was allowed to touch Toothless? It's raining out side, so he's completely soaked. He has to hear about killing dragons after he's forming a friendship with one. And as he gets his meal for the night, everyone (excluding Gobber who asks a question that's relevant to dragon training, Astrid who's being honest, and Fishlegs who's just eating) gives him a hard time; making smart ass wisecrack about his problem being that "he was there". When Hiccup gets his chicken leg and drink, Snotlout lets Hiccup know that he's not welcome to sit with them, all while wearing a really slimy grin on his face. Kind of hurts more when you realize that Snotlout is Hiccup's cousin (if going by the books), and is vehemently shunning his own blood.
And during all of that, Hiccup doesn't even try to sit with them, knowing that it will be useless. A subtle implication that this kind of thing has always happened to him so much that he has become used to it.
Stoick, after learning of Hiccup's accomplishments, praises him for it and even tells his son on how he thought Hiccup would be "the worst Viking that ever lived". Then, you can see Hiccup wih a shocked expression and then looks down at the floor with a sad expression. Stoick was trying to make Hiccup feel proud, but ended up (in a way) hurting his only child's feelings.
Even more sadder? Hiccup always knew that his father wanted him to be different, but it never crossed his mind that his DAD considered him "the worst Viking".
Hiccup's whole life in his village. He was considered an outcast because he was scrawnier than average and he thought differently. All the kids (except Astrid and Fishlegs) around his age repeatedly made fun of him. His only friend was a man twice his age, but even he didn't understand him. Than comes his father. The Chief. His own father who wishes his son could be different. Stoick wants him to stop being himself and Hiccup has made it very clear that he knows how his father feels. To have your whole village, peers, and even your own and ONLY parent think that way your whole life. I wouldn't be surprised if Hiccup had severe depression. Which makes the whole ending even more of a happy tearjerker.
Well not really just twice the age only. Gobber is 45 years old in HTTYD 1 and is 50 years old in HTTYD 2. The age gap between Hiccup and Gobber (the only person who "befriended" the boy) is a lot bigger.
Test Drive, strangely enough. There's just so much adrenaline and emotion that it gets kind of overwhelming.
Seconded. Something about the way Hiccup just throws himself into flying through the stone structures, he and Toothless moving completely in sync.
Forbidden Friendship, even though it's possibly another strange choice. The montage of the gentle way Hiccup slowly wins Toothless' trust, culminating in Toothless allowing himself to trust Hiccup in return, alongside John Powell's incredible score can be incredibly affecting and touching.
A very subtle one after Stoic returns from the first attempt to find the Dragon Nest - Gobber says his parenting troubles are over, and he is congratulated by various villagers. If you consider things from his point of view, it leads to a rather tearjerking chain of logic, with the inevitable conclusion being that Hiccup was killed. 1. Hiccup was in Dragon Training, which is highly hazardous. 2. By all indications, he is gone. 3. Everyone seems to be HAPPY about his evident death. 4. Not only did Hiccup want to go to Dragon Training for quite a while, Stoic was the one who finally granted his wish. His face as the villagers walk past really helps drive the point home not to mention the tone in his voice when he asks Gobber.
Stoick: He's gone?
The scene in the training ring, right after Toothless rescues Hiccup. He looks so proud of himself and keeps looking back at Hiccup to see whether Hiccup was impressed by his fight, while Hiccup is so terrified that the swarming Vikings will kill Toothless.
The part where Toothless has Stoick pinned, and is about to kill him. Hiccup begs him to stop, becoming more and more desperate until he just shouts, "No... NO!" Toothless looks back at him, confused, and Hiccup is just staring, looking completely hurt and terrified.
Right before the above, Toothless hears Hiccup's cry of distress all the way in the valley. Cue Hiccup running from the now enraged dragon, and Toothless trying to climb the walls to rescue his friend.
The scene where Stoick disowns Hiccup. Hiccup pleads for him to listen for once in his life, is thrown back and told "You're not my son". Hiccup's face as he watches his father leave really helped the tears flow, as does Stoick's expression after the door closes behind him. Made a double when not only that, but the fact that Hiccup knows that his father and most of the villagers are pretty much going to get themselves killed and they won't listen to his warning.
And the way Stoick just throws Hiccup aside when his son tries to reason with... And he said those words to his only child, right before he goes into a battle where he has a high probability of dying. And Stoick knows. And he knows that the last words he said to his only living relative was beyond harsh. His expression looks like he'll go back to his son, but he can't. He has to be the Chief first. And father second.
Based on the original books, Hiccup is not only Stoicks' living relative. Snotlout is Stoick's nephew because Snotlout's father is Stoick's younger brother.
It's a brief moment, but when Hiccup and Toothless were being chased by the Red Death away into the clouds, we get a close up on Stoick looking at the chase. The look on his face just said, "Odin! Please let my only son return safe! I want to fix the bond that I helped almost shattered".
Another interpretation is seeing his only child fighting a dragon that can kill him easily. Yes, he comes from a world where teens have to (or had to) fight. But, actually seeing it? That's a special kind of pain and fear.
Especially his tiny, reckless, premature (according to the sequel) son that literally forced him into being a papa bear just to survive on a regular basis.
Stoick mourning over his son's apparent demise in the aftermath of the fight with the Red Death. Granted, we all knew Toothless saved him somehow, but the sheer despair and sorrow in Stoick's voice as he grieves over the loss of his only son feels like a punch to the gut.
Pay attention to Toothless's face as he's watching Stoick; the dragon knows he has Hiccup safe within his wings - more or less - but he does not open his wings up until Stoick apologizes. Toothless is that protective of Hiccup that the dragon will not allow the boy's father near him, after Stoick's actions, hunting the dragon's nest, awoke the Red Death and kicked off the climax. Once Stoick admits his fault, Toothless gives him back his son.
Look to the background: the reactions from the crowd of Vikings in the background aren't much happier. Even Snotlout is crying.
The entire scene is made even more of a tearjerker when shown on television, as most stations jump to commercial break RIGHT at that scene, leaving the fact that Hiccup survived to be revealed AFTER the commercial break. If it was first time someone saw the movie, they'd spend the entire commercial break thinking Hiccup had DIED...
When Hiccup wakes up and discovers that he's lost his left leg in the battle; it's even more jarring if you didn't hear Gobber imply it earlier. Not to mention, the part Hiccup tries to walk using his artificial leg and immediately stumbles is like an emotional kick to the groin.
Followed immediately by the most heartwarming moment in the movie, when Toothless catches him and gives him a look that just screams "You helped me, now I'll help you." Fire-Forged Friends, indeed.
Gift of the Night Fury
In "Gift of the Night Fury", when Hiccup builds Toothless a completely working tail. When Toothless realizes he can fly independently, he backs away from Hiccup and takes off.
...leading to a different kind of tears when he comes back with Hiccup's helmet and destroys the new tailfin, instead insisting on the original saddle and rig that requires boy and dragon to work together.
Hiccups obvious hurt at Snoggletog after he's brought all of the other dragons home, but Toothless is still missing. He even miserably asks Astrid where on earth Toothless could have gone. Given that Toothless was his first proper friend, you can see him wondering whether Tooothless stayed out of real affection or just because he needed Hiccup to fly.
A subtle moment when Hiccup thinks he hears Toothless on the roof, and rushes outside to see him, but he's not there. To make it worse, just like at the beginning of the story Hiccup slips on his prosthetic leg...but unlike the first scene, Toothless isn't there to catch him. Just a painful reminder that he may have given Toothless the means to survive on his own, but Hiccup is still very dependent on his dragon.
After all of the dragons have left in "Gift of the Night Fury", the children sadly build a snow Gronkle and tearfully hug it.