To make it on the big screen, you have to give people something spectacular. Something extraordinary. Something like Bart Simpson—full frontal. It happens early in "The Simpsons Movie," when the animated 10-year-old takes a dare from his goofball father, Homer, to skateboard naked through the streets of Springfield. Hidden by plants and picket fences, he whizzes along, past kids, down hills, through traffic lights, until, in one shocking moment, little Bart flashes his little part to the entire world.