I do something similar for pouting: "That's a good crossed arm pose, but are you thinking about what your hands are doing? Because, you know, crossing them on the top gives a different message than shoving them under your armpits, and that's different than just having them under the elbows. Also, we should really work on you 'stink eye,' too. Oooo ... that's much better! Nice work!"
The fact is that I find such displays of petulance more amusing than I probably should. However, I am rarely moved by such sulky behavior to do what the peevish person wants. Truthfully, such childish displays generally push me in the opposite direction entirely. I think about this every time I see an "I did that" sticker on a gas pump, politicians yelling "you lie" during the State of the Union, or a game spoiler dropped into a random comment.
Really, you'd be more effective if you banged both of your fists AND both of your feet on the floor.