My parents taught me a few good manners. On second thoughts, they tried in vain to teach me a lot of good manners and I learnt a few. Respect your elders, Don't lie etc. I don't recollect them trying to teach me to respect privacy of others. Their omission or my selective listening was not a catastrophe until now.
I never knock on a door before I am entering any room in my house. Growing up in a joint family means you can walk into any room without knocking. If whoever in the room wants privacy, they better lock the door. Then my gentle response was banging on the door. When we moved to another city, the apartment was so small that there were no doors to knock. When we moved from that little apartment, I was studying in a distant city and very soon was wandering around in the name of employment. The need for knocking never arose. Now, I'm older and have a family. But I still do not knock.
This weekend, I moved into a new apartment in Paris and I regret not learning this habit earlier in the first few hours of living here. I am sharing the apartment with another friend of mine. The apartment is excellent in a Parisian sort of way. Wooden floors, giant windows, a bath and a separate toilet. It is perfect for expatriates living like bachelors. But there is one hitch. The toilet do not have a lock. Yes, a few hours here and I wish I had learnt the good habit of knocking.
Good habits. However silly it might sound to you, please try to impart them to your kids. You can't imagine at present the real life scenarios where it will come in handy.