You must have observed this new feature of Facebook, now while posting any status update on Facebook Timeline you can manually set who can view your stream. Now you can enable same type of feature in your BuddyPress site.
New BuddyPress plugin BuddyPress Activity Privacy adds a privacy level in BuddyPress activity stream component which provides your BuddyPress site members to select who can read his activity before it gets posted. They can choose from Anyone, Logged In Users, My Friends, Admins Only, Only me, My Friends in Group , Group Members …etc).