Oh, hundreds. A few of the most hated include:
- "sell-out" graphic scenes that tone a book down and could easily have been omitted with no loss whatsoever, such as those in Scarlett Thomas's "The End of Mr Y"; I'm not fond of graphic scenes in general but I will deal if they fulfill a clear narrative/emtional/whatever function, as for example they do in the novels of Carl-Johan Vallgren, Keith Miller and Elizabeth Bear.
- pretentiousness of the kind where the author looks down at you rather than let you in on the joke; this is the pretentiousness of Umberto Eco as opposed to the tongue-in-cheek pretentiousness of Jasper Fforde and Tom Stoppard, which conversely I can't get enough of.
- repetitiveness, such as my all-time-favourite "swerve to avoid" recourring thrice in the space of two pages in one of the last HPs (I was so unimpressed I forget which); I only put up with it if the rewards are otherwise great, i.e. Daniel Waters's "Generation Dead" can get a bit repetitive in its descriptions at times but the plot is so original and the characters so captivating I'm just about letting him off.
- as a subsection of repetitiveness, those who seem to be able to write nothing but "x said" when referring to dialogue. I get Raven's point and do agree that when a good flow of conversation is established often one does not need descriptive hangers-on at all; however I have experienced description of dialogue which is varied, engaging and informative so it annoys me when authors don't bother to make it so.
... others include cardboard characters, lack of historical/geographical/whatever research, excessive derivatism... I could continue, you know.