Hiding in the dark, just out of sight, creeping into your peripheral vision but invisible when you turn your head to see who's there.
For parents, the boogeyman is a mythological conception that is designed to scare children into good behavior. His exact description varies from household to household, but the bottom line is that he's pretty freaking scary and you don't want to mess with him. For kids, the boogeyman hides under the bed or behind the chair, or in the closet, calmly waiting for them to turn their backs or close their eyes.
In the household of the NBA the San Antonio Spurs are the boogeyman somewhere in the room, always there, always scary, usually just out of sight, but always a terror.