My family and I were having dinner recently and while we were eating I looked over just in time to notice Sydney, who is 8 years old, making a very hostile face at one of her siblings. I had very little doubt that the sibling in question had been annoying her on purpose but the face she made was more than stern, it was actually threatening. Her eyebrows were fierce, her face was pinched, and her upper body shook with anger. Her reaction was exaggerated, and in my opinion extremely disproportionate to the offense. She looked downright mean.
Naturally, I corrected her. "Sydney, there is very little difference between showing a mean face at someone, and saying mean words to them. I'm glad you chose not to yell with your voice, but yelling with your body language isn't the answer either."
I sent her to her room, then I went up after a few minutes to talk to her. I wanted to do some good, honest listening. It's easy to skip that part. So I listened, and when it was appropriate I reaffirmed what I said before I sent her to her room. I want her to remember that her body language has a volume just like her voice and with any luck she will forget that she learned how to abuse her body language from me.