Script fics generally have me backing out faster than anything else. Even when I was required to read professional scripts for high school it was a chore because I simply didn't like the format. Badly written script 'fics' on any writing forum/website make me lose a little more faith in people. :p
Colored text and different fonts are also a given, for self-explanatory reasons.
Titles are also a quirky pet peeve of mine. If the words "chronicle", "journey", "pokémon", "legend", and [insert any region name here], could be temporarily removed from the english language, a good chunk of the fictions I see every day would be without a title. Yes, you're posting this in a pokémon sub-forum/category. We all know it's pokémon. There is no need for you to put it in the title.
Generic journeyfics also make me sigh every time I see the standard opening - kid wakes up, gets pokémon from professor, goes on journey. At this point in time I've seen them so many times I'd encourage people to actually write about different people other than starting kids. Or if the kid must start somewhere, start your fic well after he's gotten his first pokémon so you don't have to write about it much.
High school fics I avoid all the time, on a daily basis. Sorry, been there, done that, don't want to go back. Even if you've tried to be different with it, I just can't force myself to sit down and watch/read a kid go through high school with 'drama' up until graduation. My high school years were very fun and memorable, but I'd prefer that they stay behind me and remain in the dusty cobwebbed corner of my mind. There are hardly any fics I see that actually put high school in a normal light anyway.
Shipping fics I tend avoid as well. While I'm a hopless romantic, there are certain fandoms where romance doesn't interest me at all (for example, pokémon :p), and I'm only there for alternate 'what if' stories. Sometimes though, I'll click on a pairing if I think they could potentially have interesting dynamics.
Creepypasta and horror fics are actually my favorite type of story - if done right. Making my heart physically race or giving me goosebumps while I'm reading is doing it right. If there is just random blood and gore with a 'twist' it makes me want to just sigh, sit the writer down, and ask them what really made them think this was creepy/scary. I could go on all day about atmosphere, subtlety, and the use of the human psyche, but I'm not sure they'd understand until they've truly been terrified themselves. Fear of what is in front of them is not what scares people, it's largely fear of the unknown. (i.e. Is this monster nice? Will it attack me? Where did it come from? Are there more? Will I die? What will happen when I die? Is it painful?)
Dark fics are a toss-up. I've written/plotted a few out myself (currently writing one, actually) because it's almost therapeutic and puts my own emotions into perspective - but that's only for original characters that I've made. Canon characters I can't do unless the character calls for it. For instance, my eternal muse is a wonderful assortment of the
nietzsche wannabe,
misanthrope supreme, and
woobie destroyer of worlds tropes - but he didn't just wake up like that one morning, his past and current life problems made him that way. Considering what had been done to him anyway, his character pretty much calls for the darkest of dark beginnings. He makes my problems look microscopic in comparison, and it makes me feel like if he lived that long living like that, I could get over a problem or two of my own. So, all in all, I don't mind dark fics so much so long as the original character called for it. As long as the fics are credibly decent and not done for the sake of being ~edgy~ they are good reads. Bad dark fic I back out of though, because it makes me roll my eyes and even laugh on occasion about how over the top it is.
I do realize though that some people might also write dark fic to try and work themselves out of a funk, but are simply bad at writing/expressing it. So usually I'll simply back out and never touch it again rather than leave a review. (Bad Azurne, bad!)