Why is Hat-on-bed bad luck?

It seems the superstition comes from a time when people believed that evil spirits lived in the hair. This could have been believed from the static electricity that would discharge in the air when taking a hat off in a warm, dry environment. It is also believed that you don’t lay your hat where you’re going to lay your head because evil spirits spill out from hats. Another view on this custom is one of sanitary origins. Keeping the hat off from the bed also meant keeping lice from infesting the hat or the bed.