Yehudah confronted Yosef with the sharp words “For you are like Pharaoh” – who makes promises but does not keep them (Bereishit Rabbah). With this statement, Yehudah fulfilled the mandate of “You shall not pollute (tachnifu) the Land” (Bamidbar 35:33), which is a mitzva according to some. It prohibits flattering (lehachnif) a murderer on account of his good points, his power, or his family connections. In our case, since Yosef had the power to execute a person at will, similar to that of Pharaoh, Yehudah was justified in relating to him as a murderer. Therefore, he spoke to him harshly rather than flattering him.
We are admonished to avoid flattering people falsely, whether in their presence or not, and even when they act properly in general. A story recorded in the Talmud makes this point. Agrippas was the King of Judea, but his lineage was questionable. When he publicly read from the Torah on Sukkot, he cried when reaching the words, “Do not place a foreigner over you, one who is not your brother” (Devarim 17:15). In response, the sages flattered him and said, “Do not fear, for you are our brother” (Sotah 41a). Because of this lie, they were punished. No one is permitted to flatter with lies. Others may rely on what was said, and this can cause great harm.
Nevertheless, if it is a question of saving lives (piku’ach nefesh) or preserving the peace (darkei shalom), false flattery is permissible.