Strangely Sock has never come across to me as that kind of character. I know that Fitzy knows (knew) him well from his time working in the States with Sloane Stephens and Fitzy never said a bad word about him. He and Sock used to hit together.
Perhaps Fitzy was being polite and/or discreet. Or perhaps there is something more going on in Sock's life that none of us are aware of and that is affecting his results and mentality at the moment. His behaviour was out of order but I won't judge him on just this one incident.
He also behaved poorly at the French open though, telling the umpire that she was atrocious and that she was only there because of him, which does suggest a certain arrogance. Im not sure whether the possibility that he is under pressure gives him a completely free pass. Maybe he needs a bit of a break from the game to sort out the mental side.