Alvin is terrible at speaking Dragonese. That is all.
How to Cheat A Dragon's Curse
How to Twist A Dragon's Tale
A Hero's Guide to Deadly Dragons
How to Ride A Dragon's Storm
Toothless and Stormfly getting snockered on dragon-nip. Toothless claims he was in Rome, or in the chimney with his friend the senator.
How to Break a Dragon's Heart
Ug the Uglithug and the unnamed Berserker chief tell Blatant Lies about Camicazi.
How to Steal A Dragon's Sword
How to Seize A Dragon's Jewel
In How to Seize a Dragon's Jewel, Alvin the Treacherous catches Hiccup and orders a huge group of slaves to bring him forward ... So Hiccup essentially crowd-surfs them towards his doom, all the while having a sweet conversation with Stoick and completely ignoring Alvin's mother screeching at them to shut up.
Toothless' new obsession with being polite.
How to Betray A Dragon's Hero
A captive Toothless starts singing the Viking equivalent of "one hundred bottles of beer on the wall".
How to Fight A Dragon's Fury
Unintentional on the author's part; in the previous book epilogue Hiccup asserts that his Trauma Conga Line in Dragon's Hero made him ready to face the Guardians of Tomorrow because Misery Builds Character. Come the start of Dragon's Fury, we soon learn that said trauma, which involved going into the Wind of Woden, sinking with a ship and losing his cousin Snotlout, has left Hiccup with Easy Amnesia.
Toothless's celebration right after the Test Flight scene where he and Hiccup learn to fly together. Toothless blows out a fireball for himself to fly through, then sails towards it with this expression of pure, sublime bliss - and drags Hiccup along for the ride.
Hiccup: "Oh, come on".
Toothless's expression after Hiccup puts the fin on his tail for the first time. "Duuuuuude."
Not to mention his face when he first realizes something is going on back there. The range of expressions he goes through is priceless to watch.
Plus while the camera is focused on Hiccup putting the fin on, you can see in the background Toothless starting to spread his wings so you just *know* what's going to happen.
Hiccup using his intimate knowledge of dragons to seemingly "subdue" them while not actually hurting them.
Toothless depositing a half-eaten fish on Hiccup's lap - and the look on Toothless' face, as if to say, "Go ahead, eat it!". Hiccup's trying it, and forcing himself not to vomit. Then Toothless gestured for him to swallow it, to which Hiccup does the silent version of "you're serious?". And after Hiccup swallows it, Toothless licks his lips as if to ask, "Did you like it?"
Prior to that, when Toothless discovers the knife Hiccup has with him, Hiccup drops it and Toothless gestures to the lake with his head as if to say, "Get rid of it." Once Hiccup does so, Toothless immediately goes into cute mode.
The "Thank you for nothing, you useless reptile." line, delivered totally deadpan while Toothless is going through his most extreme aerobatics to try and terrify Astrid into saying sorry.
Really, the entirety of that flight. Hiccup is trying so hard to convince Astrid that Toothless is harmless, while Toothless just does the exact opposite.
Hiccup: "And now the spinning".
Hiccup's (well justified) fainting dead away after Toothless counts coup with a thunderous roar in his face, then tries to flies away. Hiccup stays awake just long enough to see Toothless go down, turns around, then drops like a stone. The whimper he makes as he goes down makes it even funnier.
Toothless vs the Terrible Terror. Toothless wins. Cutest territorial match ever.
Hiccup showing Toothless the saddle for the first time and having to chase him around to get it on.
It's even funnier if you slow down the video a little, you can easily see Toothless does a play bow and is smiling with his pupils wide. He isn't running around because he particularly objects to the saddle, he just thinks it'd be fun to make Hiccup chase him around some.
Astrid's introduction. It's practically going "LOVE INTEREST HERE" with Slo Mo flames and Hiccup's goo-goo eyes.
When Gobber is telling the recruits about how his leg and arm got eaten by dragons we get this gem from Snotlout
Snotlout: I swear I'm so angry right now! I'll avenge your beautiful hand, and your beautiful foot! I'll chop off the legs of every dragon I fight. With my FACE!
The bit when Toothless is trying to ignore Hiccup just after the fish eating scene. He notices Hiccup sitting near him and, clearly exasperated, shuffles his tail round to hide his face. Then, as Hiccup reaches out to touch, peeks from under the tail, leaving Hiccup to stroll away nonchalantly.
"You're right, you're right. You're right! I'm through with the lies. I've been making...outfits."
A few seconds later, as Astrid is trying to see what's making the noise she keeps hearing, Hiccup tries to stop her by surrendering himself. Astrid responds by taking his hand off her shoulder and snapping it. Hiccup's indignant response caps it off:
Hiccup:: Oww! Why would you do that?
Ruffnut and Tuffnut fighting over a shield.
Tuffnut: Get your hands off my shield!
Ruffnut: There's like a million shields!
Tuffnut: Take that one, it has a flower on it! Girls like flowers!
Ruffnut: *whacks Tuffnut in the face with the shield* Oops! Now this one has blood on it!
And then she hands back the shield and when the gronkle blasted them they are still fighting over the shield that she just proved she could take from him with little effort. You know then that they just fight 'cuz it's fun.
"Your butts are getting bigger, we thought you were a dragon!" "NOT that there's anything wrong with a dragon-esque fig—" *punch*
When Hiccup is found out by Astrid the deadpan tone Hiccup uses when he says "Duht-duh-duh, we're dead.". Gets even funnier when you realize that Toothless is doing a picture-perfect copy of Hiccup's eyeroll, then stomps off on his hindlegs, apparently figuring to solve the problem himself.
Hiccup imitating his father's Scottish accent.
"Excuse me, barmaid, I'm afraid you brought me the wrong offspring! I ordered an extra large boy with beefy arms, extra guts and glory on the side! This here, this is a talking fishbone!"
And then Gobber chimes in with this little gem:
Gobber: It's not so much what you look like, it's what's inside that he can't stand!
Which results in this◊ face from Hiccup, before he delivers his Catch Phrase for the first time:
Hiccup: Thank you for summing that up.
Gobber: Don't you... no, Hiccup! If you ever want to get out there to fight dragons, you need to stop all... this.
[gestures to all of Hiccup]
Hiccup: But you just pointed to all of me!
Hiccup: Dad, I can't kill dragons. Stoick: But you will kill dragons! Hiccup: No... I'm really very extra sure that I won't. Stoick: It's time, Hiccup... Hiccup: Can you not hear me? Stoick: This is serious, son. When you carry this axe [gives him an ax], you carry all of us with you. Which means you walk like us, you talk like us, you think like us. No more of [gestures to Hiccup] this. Hiccup:You just gestured to all of me. Stoick: Deal? Hiccup:This conversation is feeling very one-sided...
THIS.◊ Tuffnut's face. Took quite a few rewatches to spot—it's only on the screen for a split second, but hilarious.
"Trolls exist! They steal your socks. But only the left ones. What's up with that?"
Funny because you realized that Gobber only has one leg left. So OF COURSE his left socks go missing!
Gobber: [to Stoick} Every bit the Bone-Headed, Stubborn Viking you ever were.
And Stoick actually nods his head with an expression that says "well... can't argue with that."
When Stoick sees them arrive, you can see him mouth "What the...?"
During the climax, Fishlegs loses control of his Gronkle and it ends up faceplanting onto the beach.
Fishlegs: "I'm okay!"
*Gronkle overtilts onto Fishlegs*
Fishlegs: "Less okay!"
After the romantic flight, Astrid smacks Hiccup, then kisses him, then runs off. Now, Hiccup's dumbstruck face after the kiss is funny enough, but what sells the scene is Toothless's reaction to the whole thing. After the smack, he gives Hiccup a look that says "dude, I know, totally unfair". After the kiss, he wanders up behind Hiccup: "I think she liiiikes you, bud!" To which Hiccup's response is "What're you looking at?"
Legend of the Boneknapper
Pretty much the entirety, especially the increasing absurdity of Gobber's stories.
Which includes one of the oddest Big Damn Heroes moment ever: A hammerhead yak riding a hammerhead whale. Summoned by Thor.
Fishlegs: Uh-huh! Everyone's gonna be so surprised!
The first dragon egg explodes, blowing the door off the house it was in and sending the newborn Gronkle flying into Fishlegs' face, knocking him flat on his back.
Also in Gift of the Night Fury, when Hiccup notices that a Gronkle egg didn't get put into the water, he takes a step towards it. Look behind him, and you can see every single dragon present hurrying for cover.