There are plenty of things to be peeved about in the world of fanfiction--misspellings, bad or no punctuation, a total lack of paragraphs, badly handled dialogue, straight up bad writing, and pretty much all crossovers ever, just to name a few (and oh, does the list go on*). Here are two examples of what I call "summary peeves"--things people will say in their story summaries that will put me off a story before I've even read it.
Pet Peeve #11479a:
People who say "First fic, don't be mean" or some variation thereof in their summaries. This is actually code for "This is so bad it may actually be unreadable. I didn't use spellcheck and I don't believe in paragraphs or punctuation. If you offer constructive criticism, I will fly off the handle and threaten to kill myself because I am a sensitive artist and you are *SOB* SO MEAN!!1!!1!".
If there is a disclaimer of this type in an author's note within the story but NOT in the summary and it is clear that the author has made an effort to work with the English language instead of against it, this peeve may not apply. That first post is nerve-wracking, after all.
Pet Peeve #11479b:
People who say "Review for updates" (or, more commonly, review4updates, thus vaulting it into a whole new level of peevery**) in their summaries. This is convenient shorthand for "I am an attention whore. This story will be of indifferent quality at best, and you will not review it, hoping thereby to kill it stone dead." *Baby Peeve of the Day: Using "said" instead of "the" when referring to a recently mentioned person or object. Example: "Said girl picked up said sunglasses and put them on." I have written no less than 5 reviews today trying to politely point out that this is irritating, confusing, and jarring for the reader, and deleted them all after concluding that there is no polite way to tell people they need to Just Write Better.
As a general rule, I can pass by these without even a glance, safe in the assurance that there is nothing there worth reading and that any review I might post would merely be frothing at the mouth about the murder of the English language.
**See: Spaces Are Good and Use Real Words