I can tell you, as someone who watches him week in week out, the worst thing you can do is coach that out of him. Far better player with that 'nasty streak' in him.
I also see this comment a lot, and most people base it on the Scottish league which I can understand to a point... but, he has consistently performed in Europe against top teams, his hold up & link up play is superb. Just lacks a bit of finesse in certain situations, but that is 1 thing that could be coached.