When it's just roaring along through a kaleidoscope of Los Angeles locations, the camera perched behind, above or below the skateboarding heroes and villains, the movie can be fun. It's shot in an extravagant, try-anything, music-video style. It's rattlingly paced, vibrant and splashy. Then we get to the story. Stop me if you've heard this one: Boy meets girl; boy loses girl; boy gets girl. Sound familiar? Try this for extra spice. Two warring teen-age gangs clash--the free-and-breezy Valley Guy "Ramp Locals" and the swaggering, black leather, bone-in-the-nose "Daggers."