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 throw him and Astrid off.
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 hilariously awkward father/son 'talk' that culminates in the "breast hat" moment.
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 smiling with his puples wide. He isn't running around because he perticularly objects to the staddle, 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."
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 shied 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*
Particularly funny, because Hiccup is stroking the helmet...and then jerks his hand away immediately after being told it was part of his mother's breastplate.
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!
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!
Even funnier since all the others immediately succumbed to Cuteness Proximity at the sight of the baby Gronkle.
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.