Open an umbrella indoors and bad luck will "rain" on you. But why? There are two schools of thought: 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. http://www.csicop.org/superstition/library/umbrella.html www.fifty-five-plus.com/family/SP0028.htm

You might put yours or someone elses eye out!

When I was a child some 50 years ago... I was told that you'll have an ugly husband if you opened an unbrella indoors.

I don't know!

You will break something or injure someone because the umbrella is so large.

It's not considered bad luck by anyone with IQ in the double digits. Only morons consider it bad luck to open an umbrella indoors. (But I respect your right to believe it.) :)  

i dont know where it originates from but in hong kong its meant to be unlucky because its believed to attract or trap (bad?) spirits.. i think..

Leprachuas can't watch that way. Bad luck isn'tactually that bad.

Here is another list of guesses: https://people.howstuffworks.com/open-umbrella-indoors.htm

probably cause someone said it was bad luck