My son and I had this discussion today. He was upset with me because he didn't get his way. He had just received a consequence for disobedience and he was mad. Instead of responding to his anger and just telling him no, he wasn't going to run away, I used this opportunity to teach a life lesson in critical thinking and planning. I mean, he may still want to run away but at least now he'll be prepared when/if he does, right? ;-)
"Mommy, I'm going to run away to South America and live in the rainforest." (arms crossed, brows furrowed, pursed lips, mad face)
Me- "You are? What will you do for food?"
"I'm going to eat fruit off the trees there."
Me- "Oh, ok. Well, what about on the way there? What will you eat then...and how will you get there? Walk? That will take a long time to walk the whole way. Where will you sleep?"