Before I came to Japan I read many books on Japanese etiquette and social taboos. I guess the main one that stood out in my mind was “don’t touch your noise” the book said picking your noise or even touching it in public was a big no no. Well it took me about 2 days of being here to figure out no one told Japanese people to follow this rule.
There is a more complete list of Japanese taboos and taboo myths at
Japanese Taboos, Truth or Fiction