Things in Fanfiction that Bother Me

I've read quite a bit of fanfiction throughout the last year or two, and I've noticed some things that I like and some that I dislike. I'm going to call attention to the ones I dislike so that if you ever have a desire to write fanfic, you'll have the presence of mind to stay away from these things (or at least make it interesting in other ways) if you want me reading it.

General Fanfiction Annoyances

• Not proofread.  If you've got bad grammar, give it to someone who is a Grammar Nazi so they can look over it.  At the very least, don't post something that you haven't looked over first. It's still possible that errors will exist, of course, but it'll be better if they are kept to a minimum.
• Wish fulfillment.  OC's (own character), Mary Sue, overpowered cross-over characters, giving a canon character a twin and/or changing their gender, pairings that would never ever happen, easily defeated foes, etc. The point of fanfiction is to explore the author's world, not shove someone who doesn't belong in there to show how awesome you are. Or at least that should be the point... (Also, almost every OC ever is a "darling" that should be killed with fire and acid).
• Character bashing. Lots of us readers are very defensive of canon and don't appreciate when fanfic authors try to "fix" or destroy it.
• Mature content. Sex, slash, squickiness, language, anything that would be Rated R (and sometimes even PG-13) if it was a movie... I just don't want to read it, okay?
• No plot. If there's no conflict, then there's probably no point.
• Songfic.  To those who write these: you think you're original, but you're not. And we can't hear the music anyway. You're better off writing a poem.
• Abandoned stories. If you can't finish it, for whatever reason, please give a summary of what probably would have happened had you continued. Or, if you can, stop posting chapters when you get to a satisfactory break point. At the very least, if you know that you aren't coming back to the story, say so.
• Fanwork that does not complement original. This can be annoying both when an author sticks too close to canon or when they stray too far from it. It's hard to tell where exactly the lines are, but there shouldn't be gratuitous quoting/paraphrasing of canon, nor should there be making things so different that it would be unrecognizable if the names were changed.
• In-character commentaries on original work. The only reason I would look up a fanfic with this in it is if I didn't have the original work in front of me and I wanted to check a certain part for reference. Reactions from the characters gets old really fast and the word count ratio between the original and the new makes me want to scream.
• Internal commentary. Author notes have their place. That place is at the beginning or the end, not in the middle of a chapter. Generally comments of the "I'm so clever/funny/evil" nature are more annoying than helpful. Also, constant whining about readers reading and reviewing is likely to turn people off to your work.
• Weird POV switching.  You don't need to say "So and So's POV" at the start of every section, especially if it's in third person.  You can just say the person's name if it's first person or say nothing at all if it's third. Also, don't switch back and forth between first and third person without a good reason--it's disorienting. And please refrain from using second person if at all possible.
• Specifying what bold, bold italics, not bold italics, underlined, etc. mean. The reader should be able to figure that out by context and not have to rely on your pre-chapter specs.
• Purple prose. You don't need to say "the raven-haired maiden with wide doe eyes somnambulated through the pristine lily of the valley fields with an ethereal sigh." Use terminology that the characters themselves would use. If your character actually does use purple prose all the time, then it might be okay, but please don't give the readers too strong of a reason to gag, please.
• Unclear time-frame.  If there are time jumps, please make sure that the reader can always tell when the story is taking place.
• Freakishly short chapters. I would prefer to have several scenes all at once than have just a few hundred words at a time. Freakishly long chapters can be exhausting on occasion, but it's worse when the flow is disturbed frequently by forcing you to click the "Next" button or by the waiting in between updates.
• Here, let me tell you about this flashback... If a character is telling a long story, it's okay to go into back-story mode instead of having the character say "and then she said '[blah blah blah].' So I did [blah] and said '[blah blah blah]'..."
• Unbalanced crossovers.  When two or more universes are blended for a particular story, one character/universe should not seem completely superior/inferior to the other. Each should be able to contribute in a meaningful, non-artificial way to resolving the conflict.
• Neglected to check the facts.  Sometimes you think you know something, but it's better to double-check to make sure you're right before you add in that detail.  Wikis can be an invaluable resource for checking dates, character attributes, terminology, and sometimes can even spark a new path for you to explore.

Harry Potter-Specific Annoyances

• Pre-2007 Marauder-fics.  Snape is always OOC in these, since the "Mudblood" incident was an accident, not the norm (though the people writing then can be forgiven since no one knew that at the time). Actually, a lot of fics in this era can be annoying due to having to deal with the foregone conclusion about Wormtail.
• Superawesome Patronus and/or Animagus forms, such as a magical creature, having multiple forms, or other extra powers. And working to become an Animagus at all takes lots of time and effort that would usually be spent elsewhere unless you had a very good reason to specialize (like having a werewolf friend and not much else to worry about). Also, though I don't have any concrete evidence, I've been led to believe that a person's Animagus and Patronus forms are likely to be the same (note McGonagall and James Potter, for example), so when Harry suddenly show up as a griffin or a wolf or a snake, a little part of me shirks away. Though if Harry isn't a stag, snake probably would be the best choice, I suppose.
• Extraunique wands. Wands are already unique.  You don't need yours to have a weird core (basilisk fang, griffin feather, chimera scale, multiple cores, etc.) to make yours cool. Besides, Ollivander only sells phoenix feather, dragon heartstring, and unicorn tail hair wands because they are the best.  The only exceptions to this rule are Fleur's wand (which has Veela hair for family reasons), Sir Cadogan's wand (which has troll whisker, befitting the character's ineffectual nature) and the Elder Wand (which has thestral tail hair and is extremely choosy about who can use it).  Unless there is a very good reason not to, please keep wands normal.
• Instamastery of magical concepts. Even Hermione didn't always get it right on the first try. The main exception to this rule is if the character in question did all the leg work offscreen.
• Have fun but Obliviate to preserve the timeline when you leave.  I have seen too many stories where a bunch of next-generation characters go back in time and spend the whole time introducing themselves to their parents/grandparents while waiting for Dumbledore or someone in the future to figure out how to send them back to their time. Also, having someone stuck in the past for a year so they teach Defence Against the Dark Arts while avoiding parents finding out who they are (which, of course, fails, but they're just obliviated afterwards so who cares?) Time-travel stories tend to be more interesting when the past gets modified with significant consequences.
• Broken Time-Turner (or prototype Time-Turner an adult took home for some reason) as a means of traveling through time.  Especially to the Marauders' sixth or seventh year or to Harry's fifth year (and they always seem to materialize at Grimmauld Place, for some bizarre reason).  Actually, just conveniently easy long-range time travel in general, especially to the future--if it were easy, then all sorts of people would be destroying the timeline by now.