1. You MUST carry your 'anmeldung' (address registration) around with you everywhere to prove you are a human being.
Otherwise the post office workers and bank workers and cell phone companies will not be able to tell you are an actual person. So please... carry your official, stamped address registration with you at all times.
2. You MUST NOT request anything by way of a favor from anyone.
Sprained your ankle at the train station and want a cup of ice? NO. We do not give out ice here at McDonalds. You can't have a cup of ice because the ice is... uh... made from tap water and uh... you could get sick from it.
CODE FOR: it's none of my business and even though I work in the service industry and our ice costs nothing, I will still refuse to do anything for you. How dare you expect me to help you.
3. You MUST NOT expect that just because you paid 60 euro for a train ticket that this means you get to sit in a real actual seat. So what if there was no option to reserve seats online when you bought the ticket 3 months ago, it is not Deutsche Bahn's fault. You can stand for 2 hours or sit on the floor. That is how it works in Germany. Enjoy our renowned efficiency!
4. You MUST NOT use a giftcard on books. In fact, it is not legal for books to be put on sale unless the publisher instructs every bookstore that the book should go on sale. Books are not allowed to be sold for a discount or on sale because it causes competition and that would be a terrible thing for the German people. Having books at an affordable price--it just goes beyond thinking. No. We mustn't have that. Better that all books stay at the same price at every single book store.