Let's list some common ones:
- If you lie down quickly after eating, you will turn into a cow.
- Salt is like kryptonite to ghosts. You should throw it over your shoulder after going to a funeral.
- Don't stick your chopsticks into your food, it looks like the incense that are burned at funerals.
- You should hide your thumb if a funeral car drives past.
- If you play with fire, you will wet your bed.
- Cutting your nails at night it not good. If you do it, you will not be with your parents when they die.
- If you whistle at night, a snake will come to you. A snake, in this case means a thief. I think it's more about not bothering your neighbours.
- Being crapped on by a bird is considered lucky (strangely). It's because the うん un from うんこ sounds like 運, which is luck.
- Diarrhea and illness is caused by a cold midsection.
- Don't kill spiders in the morning, it's bad luck. At night is okay, though.
- If a stem is floating vertically in your green tea, you're lucky.
Some things in Japan are less superstitions, and more manners or etiquette.
- In a business meeting, and also at dinners, the person of highest rank sits the furthest from the door. The historical reason being that if someone busted in for an assassination, they would be safest.
- The numbers 4 and 9 are sometimes unlucky, so one should never give gifts in 4s.
Know any others?