Open an umbrella indoors and bad luck will "rain" on you. But why?
The most common stems from the days when umbrellas were used mainly as protection against the sun. To open one indoors would be to insult the local sun god (especially Ra) and invite his wrath on everyone in your household.
Another theory borrows from the idea of an umbrella as a protector against the storms of life. If you were to open one in your home, the household guardian spirits might think you felt their protection was insufficient, and then they'd leave in a huff. Once again, everyone in the house is cursed.
In truth, the superstition is probably coincidental. (Someone left his umbrella opened in the hall and had a terrible day--he told his friend to keep their umbrellas shut, and it spread.)
It isn't always bad luck to open an umbrella inside. According to some, it's only considered bad if any of the following apply:
-The umbrella was a gift.
-The umbrella is black.
-The umbrella has never been used outdoors.
-There is a sick person in the house.
Other bad luck umbrella superstitions:
-Never give an umbrella as a gift.
-Never pick up an umbrella you dropped (ask someone to do it for you).
-Never place your umbrella on a table or a bed.
-If a single woman drops her umbrella, she'll never marry
- Black cats
- Putting shoes on a table
- Stepping on cracks.
- Walking under ladders.
There are many more but none have been proven to be true.