It would probably be better to have a greet method. The idea is that the user doesn't need to know that $this->greet is an array.
So:
class Greeting {
protected $greet = array('Hi','Hello', 'Howzit', 'Ola', 'Whats up');
protected $name='You';
function __construct($name) {
$this->name = $name;
}
function greet(){
shuffle($this->greet);
echo "{$this->greet[0]} {$this->name}!";
}
}
$hi = new Greeting('INSERTNAMEHERE');/*NAME OF PERSON GOES HERE*/
$hi->greet();