1. [all fandoms] There is no reason to assume that all slash is lower quality, that every slash writer is fixated on getting two guys or girls into bed, or that not shipping at all somehow makes you a purer, better, more devoted fan. They're all silly assumptions that don't mean anything when you come right down to it. But people always like to feel superior for superficial reasons. I think, in fandom, you only have good reason to feel superior is your art/writing/designing is top of the line. Not because you find slash unfounded, worship canon, or write het exclusively. [ETA: Or write slash exclusively, for that matter...]
2. [all fandoms] There's no reason for the BNF (Big Name Fan) to be a species in existence. Of course there are some fic writers and fan artists who are going to be more prominent and attract more attention, but there's no reason to fawn over them. Popularity is not linked to personality and, as Lew has noted, work that is liked and accepted by the masses is often bland and unoriginal enough in order to appeal to so many people. Thus, this false appearance of superiority seems like nothing but the flauntings of a flawed peacock. [ETA: In other words, it's weird to devote more time to another amatuer's work than the original series it stemmed from. This leads to a line blurring between canon and fanon which is irritating and disturbing.]
3. [Charlie's Angels] Dylan/The Thin Man is not a feasible pairing for those looking to write romantic and fluffy fanfic. If anything it is a twisted, strange pairing, suitable for one night stands and perhaps violent, hair-pulling sex. It is not a domestic relationship. The Thin Man is not a nice person; he's an assassin with an exceptionally nasty hair fetish who doesn't speak and who spent a few years as a wild child before growing up among nuns. He's not all bad, as evidenced by the contributions he continues to give to the church, but that doesn't make him a good guy by any means. There is no true conformation that he switched sides. So lose the roses and candy hearts, people, and leave The Thin Man alone.
4. [Harry Potter] Remus/Sirius is not canon. There is no reason or evidence for this topic to even come up. Deal with it.
5. [all fandoms] Most humor fics are not funny. If it's written by anyone under 21, there is no way I'm reading it. Inside jokes are not funny. And if your friends think you're funny... no one else does.
6. [Discworld and Good Omens] Trying to write like Terry Pratchett is bad. No one writes like Pterry except Pterry. Footnotes do not help a fanfic and are often clearly unnecessary.
7. [Back to the Future] Most BttF fanfiction is downright awful. Flaming Trails is either stupid or has Dissociative Identity Disorder. I don't know which. I suspect both.
8. [The Faculty] There's no good reason for Casey/Zeke. It's just fun. :D
9. [Lord of the Rings] There's no good reason for Aragorn/Legolas. But it isn't fun. It's completely stupid. And I've written it! But I believe all A/L fangirls should be round up and shot in the head.
10. [Harry Potter] Remus Lupin is a werewolf. BIG, FIERCE, VIOLENT BEASTIE. He's not an uke. He is perfectly capable of taking care of himself. He's not super attractive and he doesn't have long, flow-y hair. >_> He should look like Jeremy Irons.
And here's an extra one that I left off the "official" list because I felt it too self-important and vain. I still think it's true.
11. [Willard] There is no canonical evidence to support the concept of Willard being raped or otherwise sexually assaulted in his lifetime. This is something I came up with because I'm a sick little bastard child who finds Willard!torture attractive. This doesn't even come under the heading of fanon. It's one idea I had. Don't take it as fact. I'm not trying to say "don't steal my idea" ... I'm trying to say that it's better to find your own interpretation of the movie than use mine.
[ETA: 12. [all fandoms] Major out of character behavior. Most people get sick of this. There are fics that make logical progression from an approximation of the original character's personality to whomever it is they really want to write about. And that's not so bad. A good writer can make it work rather beautifully (I actually read a Snape/Harry fic last night that I didn't hate, and I find that a minor achievement in and of itself) to show growth in the characters and in their interaction. It's also good for expanding minor characters who aren't well defined in canon. This is why movies are fun to write fic for, because you tend to have limited character development in the two hours it takes to tell the main story. But if you're going to toy with someone else's character like a puppet, making them do or say things they never would, then why bother writing fanfic at all? (Because no one would read your original fiction, perhaps?)](
I get a little mean. But fandom is stupid, stupid, stupid. And I'm feeling a little mean. Hahaha. I like this icon. Prozzak rulez.