One thing that I remember making me laugh out loud was on the fourth book, while Harry and Ron were making up predictions for their Divination class. I just love this whole dialogue between them, especially the last few lines. haha
I'll spoiler tag it, just to make sure.
times he had run his fingers through it in frustration, “I think it’s back to the old Divination standby.” “What — make it up?” “Yeah,” said Ron, sweeping the jumble of scrawled notes off the table, dipping his pen into some ink, and starting to write. “Next Monday,” he said as he scribbled, “I am likely to develop a cough, owing to the unlucky conjunction of Mars and Jupiter.” He looked up at Harry. “You know her — just put in loads of misery, she’ll lap it up.” “Right,” said Harry, crumpling up his first attempt and lobbing it over the heads of a group of chattering first years into the fire. “Okay . . . on Monday, I will be in danger of — er — burns.” “Yeah, you will be,” said Ron darkly, “we’re seeing the skrewts again on Monday. Okay, Tuesday, I’ll . . . erm . . .” “Lose a treasured possession,” said Harry, who was flicking through Unfogging the Future for ideas. “Good one,” said Ron, copying it down. “Because of . . . erm . . . Mercury. Why don’t you get stabbed in the back by someone you thought was a friend?” “Yeah . . . cool . . .” said Harry, scribbling it down, “because . . . Venus is in the twelfth house.” “And on Wednesday, I think I’ll come off worst in a fight.” “Aaah, I was going to have a fight. Okay, I’ll lose a bet.” “Yeah, you’ll be betting I’ll win my fight. . . .” They continued to make up predictions (which grew steadily more tragic) for another hour, while the common room around them slowly emptied as people went up to bed.