「バカは風邪ひかない」- Baka wa kaze hikanai

"Stupids can't catch colds"

It may sound weird, but if you catch a cold in Japan and someone tells you that, you should thank them. They are saying in a polite way that you're wise/smart.

Also, when someone sneezes, there is no expression such as "God bless you" in Japanese - in fact, it's considered a bit embarrassing to sneeze in public and people will often pretend they didn't see it. And the one who sneezed is supposed to say "shitsureishimashita" (a close translation would be something like "I'm sorry for my rudeness").

「夜 に 唇 を 吹く と 蛇 が 来る」 - Yoru ni kuchibiru wo fuku to hebi ga kuru

"If you whistle at night, a snake will come at you"

During the Edo period (also known as the Tokugawa period, the historical period between 1603 and 1868), thieves used to communicate and warn each other by whistling. As a result, whistling at night nowadays is associated with inviting burglars (the snake) into your place.