Ignoring a user

After selecting the chatter's name from the user’s list (or from their profile), choose "Ignore User" and be sure to confirm by pressing “Yes” button at the top.
Any messages from them will be ignored. They will not know you are not getting their messages.

To remove a person from your ignore list, click the Site Users menu then choose "Ignored".
Use the three button menu to the right of their name and choose “Unignore”.