Musar zu Schemuel I 25:3

ולא יכלו דברו לשלום . Rashi comments that we can learn the praiseworthy character traits of the brothers from the very criticism the Torah directs at them. The brothers were no hypocrites, fawning on Joseph to his face and cursing him behind his back. They were candid and frank. We have a parallel to this frankness in Samuel I 25,3, where Naval is described. Our sages say that he was just as evil as is implied by his very name [hardly a name given to him by his father at birth. Ed.], i.e. he did not bother to conceal his עין הרע, ill-will. The difference between Naval and the brothers was that whereas Naval was offensive to everybody, the brothers refrained from speaking to Joseph altogether. They did not want to be guilty of hypocrisy by speaking to him peacefully, hiding what was in their hearts; they also did not want to be guilty of hateful behavior towards him.