My son has started the habbit of hitting. Even standing at the car window getting his attention he will sit and try to swipe at you through the glass etc. I've tried all I can think of from a firm 'no' to telling him that hittings bad and leaving him in his room for 5 mins. Nothing seems to work and I don't want to tap his hand as he will think because I'm doing it to him he can do it to whoever he wants. He has a party soon and I don't want him trying to hit any other children there as well as anywhere else. Not sure if its just a phase or something else. But has to stop. Help?