Map: "Mister Moony presents his compliments to Professor Snape, and begs him to keep his abnormally large nose out of other people's business. Mister Prongs agrees with Mister Moony, and would like to add that Professor Snape is an ugly git. Mister Padfoot would like to register his astonishment that an idiot like that ever became a professor. Mister Wormtail bids Professor Snape good day, and advises him to wash his hair, the slimeball."
Especially since Lupin gets to read it.
And especially since he's Moony. Knowing that the normally polite Lupin had the first insult there...
Harry's reaction, which is basically halfway between breaking down laughing and shitting himself in terror.
Later on, at Christmas, Dumbledore seemingly gets in a little dig at this when he gets Snape to pull a Christmas Cracker - and out pops a stuffed-vulture hat. Which Dumbledore then cheerfully dons himself.
Speaking of boggarts, there's also Herminone's taking the form of Professor McGonagall who told her she failed every subject. Even Ron couldn't stop laughing.
If there are some readers who think the Quidditch scene's a bit dull, the commentaries of them at least were generally very entertaining. Remember Lee Jordan's opiniated commentary on the particularly brutal Quidditch final?
Lee: THIRTY-ZERO! TAKE THAT, YOU DIRTY, CHEATING— McGonagall: Jordan, if you can't commentate in an unbiased way—! Lee: I'm telling it like it is, professor! ... Lee" [after Malfoy grabs the end of Harry's broomstick to prevent him from catching the snitch] YOU CHEATING SCUM! YOU FILTHY, CHEATING B-- McGonagall: [Not even bothering to tell him off, as she was pointing her finger in Malfoy's direction, her hat had fallen off, and she too was shouting furiously.]
And the mention of Lee swearing so badly into the microphone that McGonagall tries to take it off of him. Also, his hitting on Angelina Johnson when she gets the Quaffle.
Earlier, when Harry gets caught in Hogsmede by Draco Malfoy, who then tells Snape: "What is your head doing in Hogsmeade? Your head is not allowed in Hogsmeade. No part of your body is allowed in Hogsmeade."
After the disastrous Quidditch match, Harry asks where Oliver Wood is, and Fred replies: "He's still in the showers. We think he's trying to drown himself."
The "Monster Book of Monsters," especially the comment by the manager of Flourish and Blotts, the Wizard book shop:
"I thought we'd seen the worst when we ordered two-hundred copies of "The Invisible Book of Invisibility." Cost a fortune and we never found them!"
Percy held out his hand solemnly as though he and Harry had never met and said "Harry. How nice to see you."
"Hello Percy," said Harry, trying not to laugh.
"I hope you're well," said Percy pompously, shaking hands. It was rather like being introduced to the mayor.
"Very well thanks-"
"Harry!" said Fred, elbowing Percy out of the way and bowing deeply. "Simply splendid to see you old boy-"
"Marvellous," said George, pushing Fred aside and seizing Harry's hand in turn. "Absolutely spiffing."
"That's enough now," said Mrs. Weasely.
"Mum!" said Fred, as though he'd only just spotted her, and seized her hand too. "How really corking to see you!"
A couple of pages later... Mr. Weasely says that the Ministry are providing cars to take them to King's Cross and Percy asks why.
"It's because of you, Perce," said George seriously. "And there'll be little flags on the bonnets with HB on them-"
"For Humungous Bighead," said Fred.
It gets even better when you realized the following description "Everyone except Percy and Mrs. Weasley snorted" includes Mr. Weasley.
Also, Percy going mental at Ron and tearing their rooms apart when Fred and George nick his Head Boy Badge and change it to say 'Bighead Boy'
It's all too satisfying to see Malfoy and his crew owned by Harry's Patronus spell when they dress up as dementors and go out into the field trying to scare Harry. It's even more satisfying to see them get owned again by Professor McGonagall after the match.
Another McGonagall moment: "Tripe, Sibyl?" And this:
McGonagall: I hardly think that matters, Sybil, unless a mad axeman is waiting outside the doors to slaughter the first into the entrance hall."
"...and Ginny Weasley, blushing furiously, turned up with a get-well card she had made herself, which sang shrilly unless Harry kept it shut under his bowl of fruit."
When the Gryffindors return to the common room after Ron's been attacked by Sirius Black, Fred immediately says "Excellent, are we carrying on [with the post-game party]?"
Snape giving Ron a detention of washing the Hospital Wing bedpans. Ron's response is to wonder why Sirius Black hadn't hidden in Snape's office when he broke into the castle, because, "Then [Black] could have finished [Snape] off for us!"
After months and months of learning to 'care' for the insanely-boring Flobberworms by poking lettuce down their throats, Ron tries to cheer up a despondent Hagrid by asking "How are the flobberworms?" Hagrid's answer: "Dead. Too much lettuce."
Meta example: Dean's boggart being a disembodied living hand can be pretty funny for anyone who played Ocarina of Time and got scared by the Wallmasters, even if it takes place 5 years before the game was released.
From the film:
The UST between Hermione and Ron in Prisoner of Azkaban. The first is during the lecture where Buckbeak is introduced and Hermione, in a panic, grabs Ron's hand. He proceeds to give her this amazed look, and she shoots him a glance that says "Don't you say a word". The second is when they're visiting the Shrieking Shack, and Hermione asks if he wants to get closer. After a short uncomfortable pause, she specifies that she meant closer to the shack.
Pretty much all of Harry's confusion at going back in time, since Hermione takes her sweet time telling him in the movie, but the best part being right after he sees his past self for the first time.
Harry (two seconds away from freaking out): "This is not normal.
Dumbledore can make a simple "good night" funny.
Harry:He's free. We did it.
Dumbledore: Did what? Good night.
Bill Corbet: Heh, Grandpa's off his meds again.
Remember the really annoying Running Gag from earlier in that scene? The elderly man in the portrait who was constantly aroused, and subsequently annoyed by Harry's shining Lumos on the walls and would constantly tell him to "Put out that light"? Well, here's where a Running Gag gets turned into a Crowning Moment of Funny when Snape, after just being humiliated by the Marauder's Map, his confidence dashed, and being utterly degraded by being proven wrong by a longtime rival, gets his head chewed off by the same portrait of an elderly man in pajamas for shining the Lumos spell right in its face. Snape obeys, but with a look of what could be only Tranquil Fury on his face.
Portrait of Old Man: Are you deaf? Put that light out!
Lupin's response to Neville naming Professor Snape as his greatest fear: "Snape. [nodding] Frightens us all."
Hermione, all pissed off, threatening Malfoy with her wand against a rock wall. She gets to calm down a little and turns her back on him. Malfoy almost immediately recovers his smug look just before she delivers a punch to his face.
Hermione: That felt good.
Ron: Not good, brilliant.
In the scene where Hermione is getting the Time Turner ready to use, Harry, curious, reaches out for it. Hermione promptly slaps his hand without looking up from the device, or even breaking the stride of her speech.
When Hermione is looking at herself from behind while their present selves are hiding behind the pumpkin patch.
Hermione: Does my hair really look like that from behind?
Sirius's deadpan remarks about how James used to think he was more agreeable as a dog but however he doesn't like getting fleas are rather entertaining.
The scene where an invisible Harry attacks Malfoy, Crabbe and Goyle outside the Shrieking Shack.
The Fat Lady painting holding everyone up just to show off to the students that her voice can break the glass she's holding, much to their exasperation. It doesn't work, and instead of giving up and letting them in, she cheats by smashing the glass from the pillar next to her, and pretends that her voice really did break the glass. No one is impressed.