It’s a hidden feature which can be enabled by following these steps:
- Open your account on Facebook.
- Click on the “Chat” option which is present on the lower right side of your profile.
- There you will find two options. Choose “Friend List”.
- There you will find an option of creating a new list. Name it, for example, “Blacklisted”.
- Now, select or write the names of the people with whom you don’t want to chat.
- Set the status as offline for this chosen list.