$bob = User::where('username', 'john')->first();
$alice = User::where('username', 'alice')->first();

User::filterFollowingsOf($bob)->get(); // You will get no results.
User::filterUnfollowingsOf($bob)->get(); // You will get Alice.

$bob->follow($alice);
User::filterFollowingsOf($bob)->get(); // You will get Alice as result.