Why is it considered unlucky to leave a hat on the bed?

Although the exact origins of this superstition are lost to history, it's believed to have started because people thought that evil spirits live in the hair. Most likely, these evil spirits were actually static buildup. As people went indoors and removed their hats, the static electricity in their hair popped and crackled, a reaction attributed to the spirits that lurked among their locks and in their hats. By laying a hat on the bed, those same evil spirits would transfer onto the very place where they'd lay their heads at night [source: Today].

While there aren't any records of anyone dying or encountering evil spirits after laying a hat upside down on a bed, there may have been a good reason to avoid the practice: head lice. People may have believed that placing a hat on a bed, particularly the hat of a guest, made them susceptible to head lice that migrated from the hat to the bed.

A hat on the bed had the same connotation for cowboys. For this group, putting a cowboy hat on a bed was said to invite mischievous bad luck at best and at worst, foretell of an injury or even death. This superstition began during a time where, like most others, cowboys only bathed about once a month. Like all other hats, cowboy hats were an easy way to spread the itchy pests that came with poor hygiene. [source: American Cowboy].

In modern times in the United States alone, an estimated 12 million lice outbreaks occur annually in children aged 3 to 11. To make matters worse, lice can be spread through contact with clothing — including hats [source: CDC].

Waking up to a head full of lice — or evil spirits — the day after a hat was put on your bed would give new dimension to having a "bad hair day."