I don't feel Smart did anything that hasn't been done to him all year long. Smart plays a brand of basketball that gets on the nerves of his opponents. He defends very hard almost every play, plus he is a starter against the NBA's best players.
Cousins was annoyed to the point of just throwing him to the floor in frustration. He is learning what is allowable from the NBA opposition he plays against. Labron simply pushed him out of the way when his defense became stifling, and no offensive foul was called, welcome to the NBA rook. I've seen him get "popped in the chops" many times from many different players he was "bothering" and not say a word, because he must understand, that's the world he plays in.
The elbow Smart used may have been questionable, and I don't want this game to turn into Hockey with a round ball, But I've also witnessed players like Tony Allen, Ron Artest, Kevin Garnett do very similar stunts, and we just shrug it off. Marcus has to be tired of receiving, and decided to give back. Shame on him.
In years to come if you add the right pieces, and build a team that plays D like Marcus does, you will win many more that you loose.