The obligation to reprove one’s fellow Jew does not apply to a non-observant Jew who is in the category of a mumar (one who is aware of halachic requirements and ignores them – see Day 14). However, a non-observant Jew who sins out ignorance must be instructed gently regarding loshon hora. The beauty of shmiras halashon can be appreciated even by those whose observance level is minimal, and should be shared with them at the earliest opportunity.
Nevertheless, one does not rebuke a non-observant person with whom he does not have a relationship. It is obvious that such reproof will not convince the person to refrain from speaking loshon hora in the future, and will only serve to anger him. This would be similar to the situation (in Day 93) where reproof would cause worse sin to occur and is therefore inappropriate.
This rule holds true for an observant Jew as well. It is wrong to offer rebuke to someone with whom one has no real relationship, if it is clear that he will not change his ways and that he be offended by the person’s meddling in his affairs.
Rebuke in such a case would cause hatred and, possibly, even more loshon hora.