Djokovic is a very gracious loser, far better than any of the other top guys. So much so that it's actually a little unsettling at times. He almost looks happy after losing e.g. US Open 2010. Ironically, when he wins I find he looks quite sombre (other than the post-match celebrations). Especially when he beats Nadal/Federer.
You can't deny though that he hugely exaggerates his body language. Multiple times in his last three matches this week I was convinced he was physically toast only for him to be running around like a rabbit a little while later. I don't think he was faking; that's just silly. Why would you fake when you're completely in control of a match? But he definitely needs to control his body language. It's not cheating but it's bad play to behave like that. Murray is very guilty of this too. You'd think he has 10 different injuries over the course of a match sometimes.
On court it's Federer. Off court it's Djokovic/Murray
I would agree with this except I don't think you can include Murray yet
. Players behave differently when they're winning and when they're losing. Everyone thought Federer was a saint '03-'06 until he started losing more matches. Then his petulant side started to show more. Equally, we can't know how Murray will behave when and if he wins grand slams and becomes top dog. Even with Djokovic we have to see how he starts behaving when he declines. Nadal for example, was Mr Humble on the way up to the #1 ranking but the way back down has shown he can bitch with the best of them.