Did he? It looked to me that he was just pissed off with hsi own performance and it peaked with that misplaced pass. In a moment of extreme frustration he didn't realise the ball was coming back his way.
I think its bollocks to say he couldn't be arsed or wanted to come off, just because he doesn't chase everythinf full pelt for 90 mins doesn't mean he doesn't care as a professional, if anything id say his reaction shows he does care.
If anything i'm surprised people aren't moaning at Moyes for taking him off at that moment allowing the crowd to boo him off. As chico said in the match thread, he is still one of our most likely players to do soemthing even on a bad day.