In this segment, the Chofetz Chaim offers an example of a person whom you heard plotting to harm or embarrass someone. Certainly if the threat is serious then it must be reported, for there is a clear constructive purpose in warning the person. But if the person who spoke was just venting his anger with no intention of following through on his threat, then there is no constructive purpose. To the contrary, the report will only infuriate the subject and cause more animosity between him and the person who spoke against him.
To judge whether or not there is a constructive purpose in relating rechilus, one needs to carefully examine the situation and use a generous dose of common sense. The Chofetz Chaim offers some criteria for assessing the seriousness of any threats we may hear. The first is to know the person making the threat. Has he taken revenge on others in the past? Is he known to carry out his threats? Has he ever done before what he now claims he is planning to do? If after sizing up the situation the threat seems credible, then the information must be reported to the potential victim, assuming the conditions of toeles (constructive purpose) have been fulfilled.
The Chofetz Chaim cautions us that our first step should be to attempt to reprove the person who made the threat in the hope that this will convince him to retract it. If the situation can be resolved with that one step, it will not be necessary to warn the potential victim and disrupt the relationship. However, one need not reprove in a case where it seems obvious that the person will ignore reproof.
The Chofetz Chaim further cautions us that before reporting to the potential victim, one should try to assess what his reaction will be. If he will react by taking steps to protect himself, or by avoiding his attacker entirely, then he should be forewarned. But if his reaction will be to become enraged and confront the other person, resulting in a full-scale feud, then it would be best to remain silent on the matter.
In general, much common sense is required to decide when a negative comment should be repeated.