How Violet convinces the Slytherins to meet with the other houses.
"There will be ice cream," Violet said, very seriously.
The Wand Alarms from Weasley's Wizard Wheezes, which causes a wand to shout "HELP! HELP! I'M BEING STOLEN!" if anyone but its owner touches it — and which, of course, turn out to be no help at all because they're accidentally set off so many times that when a wand is stolen everybody just thinks it's another false alarm.
"You... you entombed your missus... here in the dungeons?"
Ophilia talking to the Marauder's Map. Moony, Padfoot and Prongs stick to being smart-arses, while Wormtail keeps hitting on her.
This exchange between Teddy and Neville;
Teddy: Girls are following me around. Even older girls!
Neville: *grinning* How awful.
Ravenclaw loses the match against Hufflepuff because the Ravenclaw Seeker's Wand Alarm goes off, distracting him and allowing the Hufflepuff Seeker to catch the Snitch. Kai is disgruntled, and Dewey gets a truly beautiful bit of snark in:
Kai: Honestly, why don't we just ban the bloody things and be done with it? No one even pays attention to them anymore!