I've been reading since I was three years old. In first grade, they tested me and found that I was reading easily at high-school level, and I've never looked back since.
In all that time, I've done me some reading---I honestly have no idea how many books I've read in my lifetime, but it'd be well up into the thousands, at least. My tastes are omnivorous, although I do favor science fiction, mysteries and historical fiction when reading fiction, and history, true-crime and anthropology in my non-fiction. And, what with all that reading, I've developed a few pet peeves. Things that'll turn me well and truly off a book, even one that I want to enjoy.
One of these things is sloppy research, particularly in historical fiction. I very much wanted to like L.A. Myers' Bloody Jack series---the concept struck me as intriguing, and Mary "Jacky" Faber is a very likeable character. Unfortunately, early on in the first book, I was noticing things that just were not right for the time period (the book starts sometime around 1805; Mary Faber tells us that she's reading the cartoons about Nelson's death at Trafalgar to her mates in the gang of street urchins she joined after her parents died suddenly.)
For starters: One character is mentioned as being willing to sell his body in advance to a "resurrection man" to be dissected after his death. WRONG! People back then were touchy about burial, and while the "sack-em-up men" were known to be around, they were regarded with horror and dread by anybody who'd lost a loved one. Since post-mortem dissection was one of the indignities inflicted on hanged criminals, nobody wanted it to happen to them, or to their nearest and dearest.
Another thing that's wrong is having "Bloody Jack" and her shipmates (she's posing as a boy and joined the Royal Navy as a ship's boy) fighting pirates---not Barbary raiders or East Asian pirates, who were very rife at that time, but Caribbean pirates very much in the mold of Blackbeard and his ilk. While small-scale sea robbery has always been a problem, and the Caribbean is well-suited to such activity, any crew like the one she encounters would be an anachronism almost as bad as having her run into a steamship in 1805. The last of the big pirates were pretty-much mopped up by the 1720s. and the "Golden Age of Piracy" was long gone by Napoleon's time.
For reasons like this, I have a hard time enjoying these books, although, as I have said, Mary "Jacky" Faber is a character it's hard not to like.
Another one that annoys me enormously is having Nazi villains, unless the story is specifically set in the period between 1920 and 1945, or in an alternate time-line where the Third Reich somehow-or-other survived into the modern day. This is why I will probably not read the sequel to David Palmer's Emergence, which I enjoyed very much. The sequel, Tracking features Nazi villains, in a world long past World War II where 99% of the human race is gone.
My distaste for Nazi villains outside of WWII-era or alternate-history fiction has nothing at all to do with liking the Nazis. It's more my feeling that the Nazis have been done to death and back again, and a dislike for beating a dead horse ad nauseam. I also do feel that a lot of sloppy, lazy authors can't be arsed to come up with any good villains, so they go straight for the most cliched Bad Guys in modern media. Whether it's the plotters plotting the Fourth Reich from their hidden fastnesses, or remnants of the Fuhrer's forces who've somehow or other survived unnoticed and learned nothing since 1945, it's old. I have seen a few exceptions---Frederick Forsyth's The Odessa File is one---but they are exceptions. If an author must resurrect old enemies, why not the Japanese, or even the Italians?
Yet another one is stories intended to teach a lesson or Send A Message. This even applies to stuff I agree with. If you want to send a message, use e-mail!
I could go on, but it's getting late here.