1. Hermione's logic puzzle in the Sorcerer's Stone film is nowhere to be seen.
2. Hagrid is seemingly never exonerated.
3. Harry breaks the Elder Wand before he fixes his own.
4. Where the bleeping heck is all the cool stuff in the maze?
5. The fact that Harry never tells Professor McGonagall about Professor Umbridge's punishment.
6. If Harry had opened his gift and used the mirror, Sirius might still be alive.
7. The Burrow burning down.
8. The Dursleys never get the punishment they deserve.
9. Ron and Harry get seriously mad at Hermione when she's worried the broomstick sent to him has been jinxed.
10. The fact that they don't use the Time Turner to stop Wormtail from escaping...
11. ...or that no one petrifies him.
12. You know, when Voldemort...disintegrates.
13. How Cedric's "hint" for Harry is pretty much useless.
14. Lupin never explains to Harry how he knows what the Marauder's Map is in the third film.
15. The fact that Dumbledore has no idea the freakin' Dark Lord is on the other side of Professor Quirrell's face.
16. Peeves is a no-show.
17. Every time Lockhart suggests that Harry is a fame seeker.
18. The lack of chemistry between Ginny and Harry in the movies.
19. Book Hermione never would have asked this question.
20. The fact that the actor who plays young Lily doesn't have Harry's eyes.
21. Sirius never gets another trial.
22. When Ron and Hermione don't believe Harry when he says Malfoy is up to something.
23. That scene where Ginny ties Harry's shoe.
24. Ron being mad at Harry for "putting" his name in the Goblet of Fire.
25. Harry being really dumb when it came to those damn letters.
26. Hermione fixes Harry's glasses instead of fixing his eyesight.
27. Malfoy weirdly sitting in that tree.
28. These missing house elves.
29. Every time Hermione doesn't believe Harry.
30. Neville's parents only appear in the movies in that one picture.
31. Bellatrix marks Hermione with "Mudblood."
32. When Dumbledore asks for something in return when Snape asks him to protect Lily and her family.
33. When Voldemort hugs Draco.
34. Harry deciding it's a good idea not to tell Dumbledore about his dreams.
35. When no one believes Voldemort is back in The Order of the Phoenix...
36. ...which causes his classmates to be pretty mean to him.
"I hate in Order of the Phoenix how everyone is so mean to Harry and how they bully him throughout the book (and movie). This is after he basically saved the school and fought the Dark Lord four previous times! Give Harry a break!"
37. How Kreacher was only ever portrayed as rude in the films.
38. The missing Deathday party.
39. And finally..."calmly."
Note: Some submissions have been edited for length and/or clarity.