Foreground obstruction crew
People and vehicles at airshows and airports charged with the vitally important task of obstructing photographers trying to get pictures of the aircraft. They typically wear orange shirts and/or reflective vests to enhance their visibility. They are best known for making their appearance *just* when the most interesting aircraft of the entire event is about to pass by, remaining present until they have spoiled the photo opportunity, and then returning to their lair.
Sh*t! My photo of that F-100 was spoiled by the foreground obstruction crew!