Someone wrote a book by this name. The Abarbanel on לא תשא עליו חטא explains that when admonishing someone, don’t put the sin on him, don’t call him names, but say that his actions or behavior is bad. This he can change but he can’t change himself. Also, put yourself in his place אל תדין את חבירך עד שתגיע למקומו.
I saw an interpretation ( don’t recall who said it) that one shouldn’t put, or carry לא תשא עליו , his own sin on his fellow Jew unless he’s free of it himself.
הוכיח חכם ויאהבך the Shlah Hakadosh says that when you admonish someone don’t call him a letz because he will end up to hate you, but if you call him a chacham, he will love you.
As mentioned before, labeling people by calling names should not be tolerated in the CR because it is worse than loshan hara. המכנה שם לחבירו אין לו חלק לעולם הבא.
Reb E: Then respectfully refer to him as either an “ehrliche letz” or as a “gadol among leitzim” and you will have successfully navigated the need for providing needed musar while adhering to the admonition of va’havta la’raacha ka’mocha.