Just after Meghan has told Ron, Ginny, and Luna that her brother really is Harry Potter, Ron says he doesn't believe it.
Ron: "No way, no freaking way. Come on, Meghan, there's only so much you're going to get me to believe. What's next, your dad is Sirius Black?"
Meghan (surprised): "How did you know?"
Ron, gawking: "I was joking."
Luna, matter-of-factly: "She's not."
Professor McGonagall's reaction when Sirius tells her that her favourite writer, Valentina Jett, is actually him.
The Singing Toilets prank the Pride pulls on Umbridge. So funny, that it makes Hermione unable to use her hands, because she has to cover her mouth to avoid laughing out loud.
Umbridge hanging on the Astronomy Tower and mooing.
Harry, Hermione, Draco and Meghan are laughing because they are remembering something funny about when they were little kids, from before they met the Weasleys. Ginny asks Harry, her fiance, what is so funny, and Harry asks her to "give [them] a sec[ond]." Ginny's now immortal answer?
Ginny: No secs.
Draco: What, ever? That's harsh.
Ron: Gapes at Ginny with his fork halfway to his mouth
Ron, Fred and a few others are testing a catapult to use on the Death eaters. Ron asks Hermione about a potion she is making (a really badly smelling potion Lily Potter invented when she was a teenager).
Hermione: It's coming! Keep your robes on!
Fred: Even after you're engaged, she still won't budge on that one? Fred shakes his head sadly. Harsh.
The Pack-parents have a similar moment to the above in Facing Danger:
Dumbledore: "Without the influence of the dementors, and with outside help, Azkaban is laughably easy to escape." (smiling) "As two of our number know from experience."
Remus: "There are days I can't believe I did that. Not that I ever regret it, but if I'd had any idea of the risks I was running, the danger I was getting myself into—"
Moody and Sirius guffawed, Aletha coughed into her napkin, and Danger slid under the table without even the pretense of a dropped fork as Remus turned a shade of red a Weasley would have envied. Arthur’s lips twitched, but Molly glared at him, and he stopped.
Dumbledore: “I must come here for meals more often. I have obviously been missing fascinating conversations.”
The Marauder Commandments. One can only imagine what one through ten are...
Draco: Eleventh Commandment. Thou shalt not get caught. Twelfth Commandment. When at risk of violating Eleventh Commandment, thou shalt run like hell.
The first 10 are simply the Biblical Ten Commandments.