What did hippies do when they grew up? They landed white-collar jobs, moved into suburban homes and became obsessed with the vitality of their sprawling lawns. That's why the Grass Pad's "high on grass" ad campaign is so brilliant. Perhaps 90 percent of the nursery-and-gardening megastore's desired customers have found themselves in a late-night, dorm-room smoke-out or at a Country Joe McDonald concert holding a joint. So why not appeal to those wild days of yore?