My coke/mentos grenade falls on the sherbert and explodes. Since scientists have been too busy trying to make flying cars or something, no one knew that when coke and mentos are mixed with sherbert, the result is picric acid. Spreading through the water supply, this causes all of the toilets and sinks in the mall to explode violently, killing several hundred people.
*evil laugh*
I make my escape through a vent on the wall, narrowly dodging a skateboard. Sheesh, be more careful!