Since you asked...
I don't like his timewasting between points. He knows he is breaking the rules every match but carries on doing it anyway (Djokovic is guilty of this as well), but only a few umpires have the balls to give him a time violation. He takes even longer when he's facing break points.
I don't like the fact that he jumps up and down during the coin toss and that he will stay seated when the umpire calls time and will only move after his opponent gets up. Earlier this year in Madrid Federer made Nadal get up first after the changeover by sitting after time was called. Nadal stared at him for a while then finally went.
Another example of his complete disregard for the rules is during the change of ends in a tie break. It's supposed to be continuous play but Nadal ALWAYS stops for water. Yes some other players stop as well but they do it quickly. Nadal has his own special OCD "drinking routine" with his 2 bottles that he MUST take 2 sips each from and then takes extra time to make sure they are placed perfectly on the court. He got booed by the crowd for doing this while Roddick waited at the other end of the court for him for almost a minute and a half - it may not seem like a long time but it all of his OCD timewasting habits add up and really frustrate his opponent and is pretty much gamesmanship.
Most of all I hate the part time tennis commentators like Andrew Castle banging on about "what an amazing shot that is" after he hits a run of the mill forehand down the line yet doesn't quite have the same level of excitement when his opponent does the same. Then you have Sue Barker saying "Wow look at that! He is really up for this!" when Nadal sprints to the back of the court, yet he does this in EVERY BLOODY MATCH of the year.