Pretty much everything. His strokes are offensive to the eye. His grunting is offensive to the ear. He's always scowling across the net, making excuses, complaining to the umpire about something or other. I think it all started because I fell in love with Federer so quickly when I got into tennis and it just flowed naturally into hating Nadal, but now I simply enjoy rooting against him. He's really the only player I actively dislike on tour. I used to hate Murray too (now don't get me started on his whining), but he won me over a bit when he fell just short of the mark so much and when he hooked up with Lendl and got more aggressive.

I actually think Fed complains to the umpire a fair amount when he's under pressure too.

I don't get how Djokovic has the takeback he does, turning the racquet face completely behind him, and still play at the pace of professional tennis. I know other players have a lot bigger swings, but I don't understand theirs either. I guess they prepare really early?

He has extremely early preparation, even for a professional. You can see in that video how long we waits with his racquet at the very back of his backswing, compared to Fed and Nadal who barely pause there, if it all. Beside that, it really doesn't take much extra time to turn one's wrist the opposite direction. Marat Safin had a similar technique on his forehand, as did Carlos Moya.

http://www.independent.co.uk/arts-entertainment/books/news/j-m-coetzee-opens-up-about-his-life-in-letters-to-paul-auster-8546488.html

Take that, Yousha.

Coetzee describes Federer’s best tennis as “something like the human ideal made visible” and says the experience of watching him play is “very much like my response to masterworks of art”.

amen... the very reason he is my favorite tennis player (and why fabrice santoro is up there for me, as well). there is little that is aesthetically pleasing about rafa's and djoko's games, though at their best they're as effective as roger at his.