Luna's Brutal Honesty about her attraction to Neville is made of this. For example, Luna doesn't understand aerial tag.
Luna: What if I want Neville to catch me?
From Chapter 38, Luna produces a Patronus...in the shape of a duck-billed platypus. When Ron congratulates her on having an imaginary animal for a Patronus, Hermione tells him that no, it's actually a real animal. He doesn't believe a word of it. Luna is completely straight faced, but Harry laughs so hard he almost passes out.
From Chapter 27, "This ponce is Voldemort?" What makes this even more hilarious is that it's Ron who says it.
From Chapter 34:
Hermione: What if you get struck by lightning? Ron: Hope the broom doesn't explode between your legs?
Harry contemplating how to get Sirius out of Azkaban: "Harry was tempted for a moment to just tell Fred and George that one of their heroes was locked up in Azkaban and then stand back. On the other hand, the Ministry might need that prison again some day."
Fred and George decided to prank Harry and Ginny by sending the former the infamous valentine poem of the latter. Harry and Ginny's payback? A Valentine in their name to Melissa Bulstrode, a Slytherin Prefect known for having decked a unicorn, resulting in them gaining a scary Abhorrent Admirer with Super Strength.
The best part? Melissa saw through it, but figured out they deserved it for something and decided to have fun.
In chapter 39 Harry decides to make a joke on Ron's supposed status as Heir of Gryffindor and Colin's belief no teacher would dare giving him a failing grade:
Harry *impersonating McGonagall*: "Mister Weasley, in light of your... heritage... I will accept nothing less than your best work in my class. Is that understood?"