Like Zander said, my least favorite genre would have to be Non-Fiction. I don't mind reading just about anything with a good story, but anything that's based on real life is mostly boring. I crave something new, be it realistic or otherwise, not something that is based on what is already known in human history. Non-Fiction books are just generally dull in my eyes. I love me some fantasy or science fiction though.

Hm...this is tough for me, since in general I will read just about any work of literature that anyone puts in front of me as long as I enjoy it. I have always enjoyed reading fantasy more than other genres, fiction being a close runner-up because it encompasses some of the same ideas. Non-fiction is great for me, too, I love reading the historical stuff and learning about the era that it is describing. Even mystery is pretty enjoyable for me, horror as well.

But if there's one thing that I just can not read, I guess it would have to be the kind of older fantasy books, in old English. The theme is just too hard for me to understand. I know that this does not actually describe a particular genre, but if I could give you an example then it would have to be The Once and Future King. I absolutely could not read that book, no matter how hard I tried to make myself, I couldn't do it. That's the closest thing that there is to a genre that I don't like, really.

Although I generally seek out books that are of interest to me, I don't care much for romance novels. Most of the ones I come across (or have been assigned to read) are cheesy, lame, and uninteresting. If I had the choice, I would rather have a root canal, or sit outside and watch the grass grow (maybe that's going a bit too far). I don't dislike the entire genre because I'm sure there are plenty of great romance novels out there, I'm simply saying that the ones I've come across are really awful. I definitely prefer science fiction, fiction, horror, suspense, Shakespearean works, or even fiction which I find to be fairly dull at times. I like books that delve into the realm of fantasy rather than ones that deal what is already concrete and real.

Romance by a mile. I pretty much hate any kind of Romance genre. It's boring. Either that, or I just hate it because I'm a loner lol. Probably both, if I had to guess.

Those cheap romance novels that you find in grocery stores. I tried reading one when I was bored one day a few years ago, and it was so hard. I couldn't make it past the 2nd chapter. 

thing1 :
Lexatom : I agree. Whenever it comes to movies or books that are purely romance or comedy romance, I can't stand them. However, I do love when there's a good romance aspect to a book/movie that I already enjoy.

I don't like reading books in general, but if I had to pick a least favorite genre, I'd say romance.

Honestly, I despise the Space or Science Fiction genre.

The plot of these books only arouses more questions, and are generally more barren than other books.

(Minor detail, my dislike of Star Wars may have lead to this. )

I hate books with a romance theme that are trying to be in reality. It just doesn't work, romance isn't perfect in real life, so it fits more in a fantasy setting that has tension and that leads to a happy ending.

For me, it absolutely has to do with the author of the books that I am reading. Some authors can write non fiction very well, and some can write romance very poorly. 

Overall, not depending on author, I don't really like books that are a random non fiction subject or have way too much action. I like a good character development in my books, and if the book is primarily action, there isn't room for the author to add enough side stories and other additions in order for the story to carry more than it usually does. 

I dislike most non fiction, because reading about people's lives is generally boring to me. I like reading about other worlds and lives and those that can far stretch the truth, in order to get away from my life itself and feel like I am in their world for a while. That's what makes a great book.