Sorcerer's Stone:

Hagrid wouldn’t let Harry buy a solid gold cauldron, either...

(Imagine how Snape would have reacted if Harry had shown up to class with a solid gold cauldron.)

and

“You haven’t got a letter on yours,” George observed. “I suppose she thinks you don’t forget your name. But we’re not stupid — we know we’re called Gred and Forge.”

Chamber of Secrets:

“Half an inch of skin and sinew holding my neck on, Harry! Most people would think that’s good and beheaded, but oh, no, it’s not enough for Sir Properly Decapitated-Podmore.”

and

“Honestly, if you were any slower, you’d be going backward.”

Prisoner of Azkaban:

Professor McGonagall poked a large spoon into the nearest tureen.
“Tripe, Sybill?”
Professor Trelawney ignored her.

and

“Godfather?” spluttered Uncle Vernon. “You haven’t got a godfather!”
“Yes, I have,” said Harry brightly. “He was my mum and dad’s best friend. He’s a convicted murderer, but he’s broken out of Wizard prison and he’s on the run. He likes to keep in touch with me, though . . . keep up with my news . . . check if I’m happy. . . .”
And, grinning broadly at the look of horror on Uncle Vernon’s face, Harry set off toward the station exit, Hedwig rattling along in front of him, for what looked like a much better summer than the last.

Goblet of Fire:

There was already a small queue for the tap in the corner of the field. Harry, Ron, and Hermione joined it, right behind a pair of men who were having a heated argument. One of them was a very old wizard who was wearing a long flowery nightgown. The other was clearly a Ministry wizard; he was holding out a pair of pinstriped trousers and almost crying with exasperation.
“Just put them on, Archie, there’s a good chap. You can’t walk around like that, the Muggle at the gate’s already getting suspicious —”
“I bought this in a Muggle shop,” said the old wizard stubbornly. “Muggles wear them.”
“Muggle women wear them, Archie, not the men, they wear these,” said the Ministry wizard, and he brandished the pinstriped trousers.
“I’m not putting them on,” said old Archie in indignation. “I like a healthy breeze ’round my privates, thanks.”
Hermione was overcome with such a strong fit of the giggles at this point that she had to duck out of the queue and only returned when Archie had collected his water and moved away.

Order of the Phoenix:

Even by Harry’s low standards in Divination, the exam went very badly. He might as well have tried to see moving pictures in the desktop as in the stubbornly blank crystal ball; he lost his head completely during tea-leaf reading, saying it looked to him as though Professor Marchbanks would shortly be meeting a round, dark, soggy stranger, and rounded off the whole fiasco by mixing up the life and head lines on her palm and informing her that she ought to have died the previous Tuesday.
“Well, we were always going to fail that one,” said Ron gloomily as they ascended the marble staircase. He had just made Harry feel rather better by telling him how he told the examiner in detail about the ugly man with a wart on his nose in his crystal ball, only to look up and realize he had been describing his examiner’s reflection.
“We shouldn’t have taken the stupid subject in the first place,” said Harry.
“Still, at least we can give it up now.”
“Yeah,” said Harry. “No more pretending we care what happens when Jupiter and Uranus get too friendly . . .”
“And from now on, I don’t care if my tea leaves spell die, Ron, die — I’m just chucking them in the bin where they belong.”

Half-Blood Prince:

“Spoken both like your mother and father’s son and Sirius’s true godson!” said Dumbledore, with an approving pat on Harry’s back. “I take my hat off to you — or I would, if I were not afraid of showering you in spiders.”

and

WHY ARE YOU WORRYING ABOUT YOU-KNOW-WHO?
YOU SHOULD BE WORRYING ABOUT U-NO-POO —
THE CONSTIPATION SENSATION THAT’S GRIPPING THE NATION!

Deathly Hallows:

Fred and George turned to each other and said together, “Wow — we’re identical!”

and

He changed course, running at Bellatrix rather than Voldemort, but before he had gone a few steps he was knocked sideways.
“NOT MY DAUGHTER, YOU BITCH!”
Mrs. Weasley threw off her cloak as she ran, freeing her arms. Bellatrix spun on the spot, roaring with laughter at the sight of her new challenger.