I think one of the problems is that Ronaldo does tend to come across as quite cocky anyway, and he seems to have quite a habit of diving all the time. As a result, he's got a reputation (justified or not) as being a cheat.
I've heard / read a rumour (completely unsubstantiated as most rumours are) that even his Man U team-mates are tired of his diving, and have told him to stop doing it, even in training
