Why is it inappropriate, Mom?
"Well, it's inappropriate because back in the olden days you could drive to school with gun in your car and go hunting after science class. Now -- it doesn't happen very often -- but kids who watch too many video games like to take their dad's guns to school and shoot people. The teachers don't like to be reminded of that. That's why they don't want you drawing pictures of guns."
See this thing here? It holds 5000 bullets.
"That looks like a pretty efficient gun to me, Hank, but you can't draw that at school."