The older son didn't want to rejoice about the return of the younger son. He felt that the father was unjust. He was looking down on his younger brother and wanted nothing to do with him. And even the way he referred to him, not as 'my brother', but as 'this son of yours' showed contempt both for the son and the father. The older son typified Jesus' critics, who could not accept that God would or should extend mercy to tax collectors and 'sinners'.
Anger is usually a result of feeling hurt at perceived injustices.
When it is because of perceived injustice against oneself, God is generally not pleased with this kind of anger. I'm sure the son ate many good meals at home, but he probably never asked the father for a goat, instead preferring to nurture a kind of gripe against his father. It seems he despised his father in his heart. When the father divided his inheritance between his sons, the older son never objects. He could have protested that this was not appropriate, but instead he chose to take the inheritance from his father.