What cultural faux pas should I try to avoid making in Dusseldorf?

"It is important to be aware of cultural norms when visiting Dusseldorf. It is important to be respectful of the local customs and to be aware of the local etiquette. It is considered rude to be late for appointments or social engagements, so it is important to be punctual. It is also important to dress appropriately for the occasion, as dressing too casually or too formally can be seen as disrespectful. It is also important to be aware of the local language and to avoid speaking English too loudly in public. Additionally, it is important to be aware of the local customs regarding physical contact, as it is considered inappropriate to touch someone without their permission. Finally, it is important to be aware of the local customs regarding tipping, as it is not customary to tip in Germany," remarked another expat who made the move to Dusseldorf, Germany.

What cultural faux pas should I try to avoid making in Dusseldorf?