77-year old Pat Gillespie must have looked like a vulnerable target as he unloaded groceries in front of his Flint, Mich., home last Thursday. But when a gunman swooped in to rob the Air Force veteran, the thief learned firsthand the perils of trying to steal from someone who has just returned from the supermarket. That's because instead of emptying his pockets, Gillespie reached into one of the bags and pulled out the biggest thing he could find: a 2-liter bottle of Pepsi. G…