What is impolite for Germans?

When eating, the knife is in the right hand and the fork is in the left, and it should stay this way the entire time. as in. you shouldnt put your knife down and switch the fork to the right hand. Until you finish eating

Another thing. There should always be a toast at the beginning of any meal. Don't toast with an empty glass, always touch glass with everyone (if possible), and always drink after toasting.