Dunk had issues with Barnes before Barnes even got on the pitch. Dunk wandered over to get a drink right next to Barnes when he was waiting to come on, had a few words then tapped him the side of the face. It didn't appear to be particularly friendly.
Maybe just knew that Barnes has a bit of a screw loose sometimes. I was hoping he'd get himself sent off straight away as that was always a possibility when he was hyped up for a game. Winding him up always seemed to be the best way to nullify him.