This action runs when a user rejects a friend request from another user.

 do_action('pm_friend_request_rejected', $user_id2, $user_id1);

Simple example

function profile_magic_action_on_friend_rejected($user_id2,$user_id1)

{

//do something with user 1 who rejected the friend request from user 2 here.

}

add_action( 'pm_friend_request_rejected', 'profile_magic_action_on_friend_rejected');