Listening to or Believing Lashon Hara:
Listening to Lashon Hara is generally prohibited for two reasons:
(1) It is forbidden to accept or believe Lashon Hara, and by listening to it one might cause himself to believe it.
(2) By participating in a session of Lashon Hara, the listener would be assisting the other participants to commit the sins of speaking and believing the Lashon Hara.
Believing Lashon Hara is forbidden regardless of the subject (family, friend, enemy, etc.), and regardless of the speaker (teacher, parent, spouse, etc.). Only if the subject is known to commit certain sins or have other problems, it might be permissible to believe it. In any case, someone can suspect that the Lashon Hara might be true, such that the listener should take precautions to protect himself from harm.
If information against someone might be of benefit to another (e.g. a potential business partner, roommate, etc.), it is permissible for that person to listen to it. (The listener should state why he is listening to the information so that the speaker realizes that the intentions of the listener are constructive, and also so that the speaker doesn’t intend to speak for non-constructive reasons.) However, the listener is forbidden from:
(1) accepting the information as true (he may only suspect and investigate), or
(2) taking action against the subject based on the information.
If caught in a group of people who are speaking Lashon Hara, one should try and leave the group or change the topic. If stuck there:
(1) decide in one’s heart/mind not to accept the Lashon Hara as true.
(2) do not enjoy the Lashon Hara (because the subject is being shamed, its a funny story, etc.).
(3) do not pretend to agree or accept the Lashon Hara (make a face, don’t make eye contact, or at least wear a blank expression)
If someone starts speaking Lashon Hara, try to privately and respectfully tell them that speaking Lashon Hara is forbidden. The best way to prevent others from speaking Lashon Hara is by setting a good example.