Adam Clarke on Genesis 37:4

And could not speak peaceably unto him - Does not this imply, in our use of the term, that they were continually quarrelling with him? but this is no meaning of the original: ולא יכלו דברו לשלם velo yachelu dabbero leshalom, they could not speak peace to him, i. e., they would not accost him in a friendly manner. They would not even wish him well. The eastern method of salutation is, Peace be to thee! שלום לך shalom lecha, among the Hebrews, and salam, peace, or salam kebibi, peace to thee my friend, among the Arabs. Now as peace among those nations comprehends all kinds of blessings spiritual and temporal, so they are careful not to say it to those whom they do not cordially wish well. It is not an unusual thing for an Arab or a Turk to hesitate to return the salam, if given by a Christian, or by one of whom he has not a favorable opinion: and this, in their own country, may be ever considered as a mark of hostility; not only as a proof that they do not wish you well, but that if they have an opportunity they will do you an injury. This was precisely the case with respect to Joseph's brethren: they would not give him the salam, and therefore felt themselves at liberty to take the first opportunity to injure him.