Visiting Japan, why is everyone saying "don't do this and that"?

I'm a 31yo man from the United States and I'm planning on going to Japan with my girlfriend and her sister. It will be my first time in Japan. I have no idea what to do and I'm overwhelmed with information from online forums.<br><br>We will be going for about a week in early October, staying in Tokyo for the first half of the trip and the other half in Kyoto. We're going to go to the big temples and do some shopping.<br><br>What are the top things you would recommend me not doing?