I always find it interesting that Djokovic practices with Mario (queens and toronto). I mean I know Mario gets along with everyone. but after what Mario's coach wrote about Novak on his blog...i am surprise these two still practice together. Surely, Freddie is there during those sessions.
Nole often mentions that Mario is one of his best friends on the tour. I suppose if you're already buddies then it'd take more than one specific flaw in the other guy's personality to make you stop being friends. "Ooooh, I won't be friends with you anymore unless you stop being a money whore and get a better agent!"
.. and if what you have in mind is actually "How could Nole practice when Fredrik is there," well - you can't miss that he seems to have a pretty thick skin.