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In the climax, Voldemort is ascertaining the loyalties of his returned Death Eaters, and he asks one if he's still up for a "spot of Muggle torture". This is beyond the banality of evil; this is a grandiose, faux-aristocrat Evil Overlord describing his sadistic pleasures like an outing to the seaside.
Film:
Harry's putdown to Malfoy that enrages him so much?
Harry: I don't give a damn what your father thinks, Malfoy! He's vile and cruel. And you're just pathetic.
Hermione's reactions to everything are just hilarious. Everyone in this movie is screaming their lines, but she takes the cake:
When Moody is teaching the Unforgivable Curses, Hermione knows about them but exaggeratedly refuses to explain them. And when Moody demonstrates the Cruciatus curse, she can see that Neville is seriously bothered by it, her legitimately tearful and concerned "Stop it!" in the book becomes a larynx-destroying "Stop it! Can't you see it's bothering him?! Stop it!" It's as if she knows why it's bothering Neville without having any reason to.note Neville's parents were tortured into insanity by the curse, and Moody isn't Moody but rather Barty Crouch Jr., who's showing it to Neville deliberately. We don't find this out until much later.
After Moody's lesson, Hermione rants about how horrible it is that a teacher actually dared to use the Unforgivable Curses in a classroom, and as she's talking, you can see Neville standing just a ways ahead of them with a Thousand-Yard Stare. Naturally, Hermione has to yell right as they walk past him, "I mean, did you see the look on Neville's face?" (Yes, Hermione, we did.) The timing was so spot-on, it was hilarious.
In the book, the fight between Ron and Hermione is about as much evidence of their developing romantic tension as it is a satire of teen melodrama. In the film, it's reduced to Rupert Grint sounding bored out of his mind, and Emma Watson screaming, "Ron, you spoiled EVERYTHING!"
Hermione might yell the most, but the one who yells the least appropriately is Dumbledore. It's a bit of a meme in fan circles to reference the book line "Dumbledore asked calmly", when asking Harry if put his name in the Goblet of Fire — in the film, he's interrogating him like it's Perp Sweating. Sure, there is a part where we see him clearly angry in the book, but that's only when he stopped Barty Crouch Jr. from killing Harry, and it didn't last that long, but in the movie, he yells too much, and knowing the character, not only it just makes him unrecognisable, but also means that the scene where he stops Crouch Jr. loses its impact. Some of his movements also look too forceful during some specific scenes.
Hermione's Beautiful All Along scene loses its punch when it goes from book to film. In the books, when Hermione appears at the Yule Ball, it's the first time we've ever seen her try to look really nice — up to and including magical dental work — and Harry and Ron are suitably impressed. In fact, the change was so drastic that Harry doesn't even recognize Hermione at first. In the films, though, Emma Watson had stopped the Hollywood Homely look by the second film. Daniel Radcliffe has often taken the time to laugh at the ridiculousness of it.
Almost everything about the introductions of the Beauxbatons and Durmstrang students is hilarious:
Culture Equals Costume is in full force. The Beauxbatons mesdemoiselles wear blue chapeaux and dresses, and the northern Durmstrang boys are clad in ushankas and pelts. The filmmakers made it worse by making each school single-gender, when they weren't in the book, thus tying it all in with Men Are Strong, Women Are Pretty.
Both schools, for whatever reason, make their introduction with a magical performance, each matching their respective styles, and each being incredibly bizarre and random. The girls execute some sort of kitsch dance-march, complete with a chorus of cutesy giggles and a release of hidden butterflies — which the boys promptly stomp on by bursting into the hall dead seriously, thumping the floor rythmically with magical staves, and ending with a running act of Capoeira and fire eating. Dumbledore even has a hilarious "WTF?" look on his face in the background during the Durmstrang act. The extended version takes the cake, though, with the Hogwarts students following that with a performance of the school song.
When Hagrid, Ron, and Hermione are singing the Hogwarts school song while Harry is trying to think, one can only think, "What."
At Voldemort's resurrection, Wormtail's utterly stoic demeanor while and after he cuts off his own hand, which is also completely out-of-character.
He gives himself away to his dad with his Character Tic of flicking his tongue out of his mouth like a snake (or like Miley Cyrus). It looks incredibly silly and unnatural, especially with the eye-popping expression David Tennant likes to add while doing it. Even Voldemort picks up on that tic later on. Must be a Slytherin thing.
In the Pensieve scene where he's exposed as a Death Eater, Tennant screams, "'Ello, Fahthah!" and starts making ridiculous cartoonish faces and noises as he's dragged away by the guards.
Barty Sr. is no slouch. It's particularly obvious when he doles out the four dragons in the First Task, including his very rapid "Whut'sthatboy?" when Harry seems to know about the Horntail in advance, and of course:
Barty Sr.: The Chinese Fireball, Ooohhh!
Voldemort is also really funny:
He delivers this gem to Harry when he touches his scar:
He starts making weird noises when mocking Harry's screams of agony.
He delivers a painfully straight (and unfortunately delivered) combination of Big "NO!" and Skyward Scream when Harry gets away... again. It is hilarious.
This may have been deliberate, but it's certainly Narm: when Harry returns with Cedric's corpse, nobody realizes what's happened, and the band immediately begins playing triumphant music. It takes a full 20 seconds for the band to slowly come to a halt. Even people looking straight at Harry take almost that long to figure out what's happened.
From the same scene, Amos's reaction to Cedric's death, which starts off as Narm Charm ("That's my son! That's my boy!"), becomes this with Amos's face◊ when he cries.
◊ when he cries.
