This is a fairly absurd topic, but I suppose it might be of interest uncovering obscure events that have happened at racetracks.
I was at an indoor karting track when the helmet flew off one of the pilots and rolled along the track behind the vehicle for a distance before bouncing off a tyre barrier and into the crowd. The helmet was his own and apparently not well cared for as the chin strap had sheered through. Obviously on the straight, the air came through the opening, pushed it back and it took off with nothing to hold it there.
I suppose this may have been more common in the earlier years when open face helmets and even goggles with leather caps were more common. Were there any notable cases of drivers losing headgear while racing?