I'm so tired of hearing these words!!!

"Mom!! I want that!!" It's all I hear these days. Every single toy commercial that comes on Joshua wants whatever it is! The latest? He wants one of these rc helicopters. I've tried to explain to him that it is rude to say that all the time or to demand a certain toy. He doesn't seem to get it yet. *sigh* He wants to tell everybody we know exactly what to get him for Christmas or his birthday. How do I convince him that this is not the polite way to ask for things?