「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").