Hiccup walking through fire that surprises the guard. However, he then starts panicking and calling Hiccup a demon.
Hiccup: Shh, shh, shh! I'm not a demon, I'm not a demon! (takes off his mask) See? Just a guy. Just a guy here to rescue these dragons. Guard: But you walked through fire! Hiccup: Dragon scales! Dragons shed a lot! Guard: Ohhh, I know a demon when I see one. No human legs are that skinny!
Valka and Cloudjumper watching the vikings on their mission from above. Valka tells Cloudjumper that they'd get the hang of the whole teamwork and mission thing. Cue Snoutlout messing up on his first entrance since he didn't fire-proof his butt.
Valka: (Beat) Eventually.
Ruffnut laying on the table in the dining hall and admiring her reflection from a goblet.
Gobber putting Astrid and Hiccup in a headlock and saying loudly that the two of them should think about getting married. The entire hall goes dead silent as everyone processes this and everyone turns to look at Astrid and Hiccup.
Tuffnut: The "m" word.
Ruffnut: Gross. Unless it's me.
A little after the above dining hall scene, Hiccup and Astrid talk outside, with Astrid telling him that they're nowhere near ready for marriage. Hiccup sulkily agrees while trying to stifle his disappointment.
At first he tries to stomp around on two legs, undoubtedly imitating Hiccup. And then Toothless tries impressing the Light Fury with some kind of weird Mating Dance (which is actually based on the mating dance of a bird-of-paradise), which looks utterly ridiculous. The look on the Light Fury's face makes it clear that she's thinking "Dafuq is wrong with this guy?!"
And then when Toothless gets too close to the Light Fury, she bats him in the face like a cat.
And then when the Light Fury perched herself upside down on a nearby tree branch like a bat, Toothless climbs up onto the same branch nearby and due to him misunderstanding what Hiccup was frantically telling him not to do, began to bounce up and down on the tree branch and nearly shaking the Light Fury off her perch. The branch then broke and sent Toothless to the ground, and he looked up to see the Light Fury wrapping her wings around herself in what amounted to disappointment on her face.
In a trailer scene not presented in the final film, Toothless, Hiccup and Astrid first see the Light Fury, she runs off after noticing two humans with him. Hiccup apologizes to Toothless for ruining his chances and Toothless looks back at them with a look that just screams "Seriously?"
When Grimmel comes to Hiccup's home he ask how he should address Chief Hiccup. The first time he does with an audible hiccup.
During a village meeting, Hiccup establishes the threat Grimmel poses to them and their dragons. One Berkian has this to say:
Berkian: I’ll give him a piece of my mind! And by “mind”, I mean “fists”! (punches the guy next to him)
The way Grimmel has to spell it out for the war lords which direction the Berkians and dragons are going. It's like they never looked at a compass before.
Upon seeing said drawing, the Light Fury unthinkingly steps on Toothless's linework, prompting him to growl at her. She growls back. His expression is pure Oh, Crap!.
The Light Fury flying to catch up with Hiccup and Toothless, much to Hiccup's delight... right before she proceeds to snatch him off of Toothless's back and carry him up into the sky. When Hiccup tries to ask what she's doing she ends up throwing him into the air and allowing him to fall down towards the sea. She turns back to Toothless, thoroughly pleased with herself and obviously expecting him to be as well, while in the background, Hiccup plummets to the sea below.
Toothless can only give a meek grin, looking between the Light Fury and Hiccup before diving down to save his human.
Hiccup: (while his friends laugh at him) Not a word.
During the departure from the Isle of Berk, one of the sheep (in a dragon costume) in longboat lets out a excited bleat, standing very much like a dog sticking their head out of a car window. Upon a growling green Monstrous Nightmare near it however...
"Trust me, buddy. Relationships are nothing but pain and misery." Cue getting smacked by Astrid. "What'd I just say?"
Fishlegs keeps coming back to Hiccup with a drawing of what he described as the Light Fury, and after the third attempt, Hiccup just sighs and tells him to redraw his Toothless card but white.
Fishlegs: (slightly irritated) You should have said that at the start.
Everyone starts to agree that Toothless should meet the Light Fury, with Tuffnut pointing out how sad Toothless was becoming. Hiccup turns around to see Toothless courting his own shadow, and pretending it was the Light Fury, licking the rock his shadow was casted on and rubbing up against it.
Tuffnut: Oh okay, now that's just sad... and weird.
Ruffnut: Yeah... you better do something.
Snotlout: Seriously, I would rather shovel poop all day than watch that!
Snotlout spending a good part of the movie seeking Valka’s approval. He has become a full blown teacher's pet. The way he phrases it at one point suggests he has own mother issues to work out, but it doesn't stop everyone else from noticing and finding it somewhat awkward. Especially Hiccup.
During a conversation about whether or not they should get married, Astrid jokingly redirects the conversation to suggest the next wedding they should be ready for is Snotlout and Valka's. Hiccup takes it in stride but he's clearly marked that as an area he doesn't want to think about.
At the start of the mission to infiltrate Grimmel's ship, Snotlout clearly says to the whole group, "I think we should split up." Absolutely no response from the group. Then Eret says, "I think we should split up. Just 'cause." to which Valka immediately says, "I like your instincts" and the whole group splits up.
After Hiccup and the others escape Grimmel's grasp, he stands dramatically outside watching them when Ruffnut suddenly appears beside him, noting how much she hated when Hiccup goes all heroic at that. His reaction upon seeing her is one of the few times he looks genuinely surprised at anything.
Just prior to this, Tuffnut comments "If they're stuck with Ruffnut, I'm more worried about them." Beat and then cut to Ruffnut talking a mile a minute and ticking Grimmel off.
Even when Ruffnut starts talking to one of the captive dragons, it starts shrinking away in fear of her, trying to keep as much distance between them as possible.
Finally, when Grimmel opens her cell and gives her the dragon that was in the cell next to her, he sounds so exasperated and literally begs her to leave.
Ruffnut: Okay, gods! No wonder you have gray hair. Stress is not good for you. So long, losers!
It's a thing of beauty to watch Grimmel's facial expressions change from mild annoyance at Ruffnut's never-ending flow of consciousness to someone who is constantly and desperately reminding himself not to kill his captive before he can get information out of her. One gets the feeling that him letting her go was equal parts tricking her into leading him to New Berk and jumping at the first excuse he had to make her go away.
Tuffnut and his beard. Any scene. Especially since said beard is just very long hair braids tied together under his chin.
Also, his hilarious attempts to be a "marriage therapist" for Hiccup.
"He's not going to eat your father." Just the way America Ferrera delivers the line is hysterical, as if Astrid really did believe Hiccup was going to get eaten by his own dragon in front of their children.
In a subtle way, Hiccup having to hop around on one leg during the sad and dramatic moment when they all say goodbye to their dragons. It kinda ruins the tension. It does become heartwarming as Astrid comes up to support him physically as well as emotionally.
Hiccup and Astrid's children's initial behavior when they try to get them to interact with Toothless is hilarious. Cute, but hilarious. After Astrid pushes them towards Hiccup and Toothless, the daughter's eyes keep darting back towards Astrid and the boy keeps his face covered with his hand only to keep peaking through his fingers.
Tuffnut and Ruffnut comforting Snoutlout and Fishlegs during Hiccup and Astrid's wedding is both this and Heartwarming.
of popping popcorn.