NUM430 We are forbidden to praise a wicked person. This verse forbids us to flatter a wrongdoer (Sifre). Flattering a wrongdoer is termed chanifus and is a very serious offense. Rabainu Yonah deals with this prohibition at length in Shaarey Tshuvah 3:187-199. Below are some essential excerpts: 1) The worst form of chanifus is when a person sees that someone has transgressed and tells him, "You have not done anything wrong." This will cost the transgressor to repeat his misdeeds. 2) It is considered chanifus to say that an evil person is a good man. Even if you do not actually say that his crimes were the proper thing to do, it is nevertheless wrong to praise him. The righteous despise the wicked, as it is written, "An unjust man is an abomination to the righteous" (Mishle 29:27). 3) failure to censure someone when you are in a position to do so is considered chanifus. Our Sages have said, "Whoever is able to protest against the wrong doings of his household and fails to do so, is held accountable for their behavior. If the person is able to protest against the wrongdoings of the inhabitants of his city and fails to do so, he is held accountable for their behavior. If a person is able to protest against the wrongdoings of the entire world and fails to do so, he is held accountable for their behavior" (Shabbos 44b). ... It is forbidden to flatter someone in order to take advantage of him (Orchos Tzadikim, ch. 24). Although insincere flattery is wrong, it is important that we praise others for their benefit. The late Telzer Rosh Hayeshiva, Rabbi Chayim Mordechai Katz, used to say that appreciative words help a person realize own inherent worth and will encourage him to utilize his attributes to the best of his ability. The Talmud (Eruvin 18b) states that we should say only a part of a person's praise in his presence. Excessive praise gives the appearance of being insincere flattery (Rashi). A sincere compliment, however, is a great chesed.