What should good behave in Germany?

Be polite, but not overly friendly. Germans take a look at your clothing first, then at your face, so always dress correctly in public. Respect the Germans' want of privacy and don't “invade” into their sphere unless invited; but on the other hand, if a German or German family invites you, you're expected to come and not only see that as a polite remark without meaning. Respect the Germans' sense of punctuality; being late for more than 1/4 hr (15 minutes) will be regarded as utterly inpolite, being 5 minutes early however is perfectly alright.

Germans are haircut fetishists, so make sure to visit the local “Friseur” (haircutter) at least once a month. It's also a good place to pick up some local news and chatter.

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don't mention their past as in nazi and hitler and that stuff..
be civilized and take a dictionary so you can learn the language.

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Good behaviour is good behaviour where ever you’re.

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Be polite.
At least attempt to speak German.

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Like most other places.

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Good behavior in Germany is the same as in the United Says.