Author has written 4 stories for Teen Titans, and Red Dead Redemption.
Despite my age, I am relatively new to writing fan fiction. I'm doing this mainly as an outlet for my creative energies, but in real life I have been a professional nonfiction writer. I'm not certain any of this particularly matters, but I am a 29 year old heterosexual male from Minnesota.
I figured I might as well use a portion of my profile to detail some of the things I find most annoying in fan fiction. This is going to be a work in progress, which I'll be adding to over time, and, although there are some general things which will be categorized as such, it'll be broken down by particular fandom.
Teen Titans (cartoon)
BBTerra pairings: Come on! Terra is a damn traitor. Accept it. She tried to kill the Titans for Christ's sake! Even if you say that she was under Slade's control when she almost killed Beast Boy, the fact that she was able to then kill Slade contradicts the point. If she had the ability to resist in the end, she had the ability to resist period, but she didn't until the last moment. And then if you add Things Change to the mix, she clearly doesn't give half a fuck about Beast Boy after her revival either—she doesn't even show him the respect of acknowledging who she really is. That's not the actions of a good love interest. Jillian Jackson would be a far better love interest for Beast Boy, even if she doesn't exist within the cartoon's canon (hey, they brought Sarah Simms into TTG, there's no reason Jillian can't exist within that universe's fanon as well). Raven would be a better love interest for Beast Boy than Terra—even if Raven is often verbally and physically abusive, you still know that she actually cares about him inside. Rose Wislon (who does exist in TTG, and hence within this universe's canon) would be another good pick. Various other crack pairings work (and are often quite interesting—BBJinx is a crack pairing I've found I really like, for example). But for the love of God, Terra neither is, ever was, nor ever will be an ideal match for Beast Boy.
Villainous Robin: I'm not a fan of the RobRae pairing. I am a fan of the BBRae pairing. However, I am not a fan of BBRae fics which cast Robin as a villain. For one thing, it's unnecessary—Robin has already clearly shown in the canon that he has no romantic interest in Raven whatsoever, but instead views her in the role of a trusted sibling. Also, to write Robin as a villain so directly contradicts his character that it's not even him anymore. In the original comics, Dick Grayson was kind of an asshole sometimes and could be a humongous womanizer who seemed at home with simply using women for sex and throwing them away afterward, but he was never a villain. The Dick Grayson from the cartoon does not make any great departure from that same characterization (minus the womanizing, since this was a show rated for children after all).
Poor Research: I'll just put it this way: I was once reading a fic and came to a line where it referred to Robin as having the most traumatic childhood of all the Titans. At that point, I simply stopped reading, as I lost all respect for the author. If anything, Robin's childhood, albeit very traumatic, was less traumatic than the mean for the five. If you want to delve into traumatic childhoods, Beast Boy's childhood was seriously so bad that they could never even say anything about it on the show due to the sensitivity of the target audience, and even in the TTG comics they could only briefly skim over some of it (while at the same time confirming that Beast Boy's back story from the original comics is still his back story in the cartoon's universe).
Lack of Creativity: For example, I don't even read fics where Slade is the primary villain anymore unless there's some sort of clear variance. It's been done to death. It's not interesting anymore. There's already thousands of fics on this site with a bloodthirsty irrationally evil Slade as the main villain, why don't you find another villain? Shake things up a bit? I don't like reading the same story over and over again.
Villainous Ravager: Nine times out of ten, when Rose Wilson appears in fics on this site, she's a villain. This is something that has begun to annoy me, because she's not normally a villain. In the original comics, she was only ever a villainous figure for a short time when her dad had her drugged, and she was otherwise a hardworking hero who was trying desperately to divorce herself from her father's legacy. Within the canon of the cartoon's universe, we only see Ravager once, in Teen Titans Go! #49, where, yes, she begins by trying to take over Slade's operation, but in the end Raven, Jinx, Robin and Starfire talked her into becoming a hero instead. Just because Ravager is Slade's daughter doesn't mean she has to be a villain. Raven is Trigon's daughter, is she a villain? Heck, Jericho is Slade's son, is he a villain?