Yosef brought a bad report regarding them to his father: And Yisrael loved Yosef more than all his sons because he was a son of his old age, and he made him a long sleeved tunic: His brothers saw that their father loved him more than all his brothers, and they hated him and could not speak peaceably to him.
The Ohr Hachaim explains that although Yosef told his father unkind things about his brothers, that would not necessarily cause his brothers to hate him. His brothers had the ability to discuss matters with him, to reprove him for his inappropriate behavior, and to explain that his concerns about them were incorrect. When he heard their reproof, he was sure to accept it and change his behavior.
However, once Yaakov loved Yosef more than the rest of them, and more than all of them put together, and not only that, but he also publicized his youngest son’s favor in his eyes by buying him a colorful coat that he would wear in public. Everyone knew now that Yosef was the favored son of Yaakov.
The Torah indeed tells us that only when the brothers saw that Yaakov loved Yosef more than them did they realize that they had no hope of repairing the rift between them and make peace. They then began to hate him for the stories that he said about them. Now that he was the favorite son, there was no way he would accept their reproof and change his behavior. When a child is his father’s favorite, he has the self-confidence to ignore the words of others.
Now they were in a position of וְּלֹא יָכְּלוּ דַבְּרוֹ לְּשָלֹם – they could no longer use speech to make peace with him over the stories he told about them.
