When I studied German in the early 90s, we were taught that an unmarried woman is a Fräulein, but I recently learned that Fräulein is offensive. We aren't all ugly Americans, and I don't want to fall in that category even accidentally!
What are other words or phrases that seem to have straightforward, innocent meanings but that may be off-putting to native German speakers?
Basically, if you are an obvious foreigner, most women will assume that you call them Fräulein because you are using the conventions of your own country and not take offense. This might change if you insist on it after correction.
The same thing applies to many other faux-pas in social etiquette as long as they are honest mistakes. It is not the same thing as calling someone the German version of a**hole since I won't believe you that this is polite in the US.
It is a bit hard to answer your question because it is actually an English question as well: What polite English phrases are impolite/unused/misunderstood in German?
Something that you should look out for is that Americans can actually be "too friendly" for German speakers, as in superficially friendly and not meaning it. Your "polite" may be someone else's "hypocritical" and someone else's "honesty" can be "rudeness" for you. (But take this with a grain of salt because my knowledge of US norms is spotty.)
E.g. I will certainly not tell you that you are welcome to visit me if you come to my city if I don't mean it.
This is a great problem because people will perceive it as your character (and vice versa) and so they will not explain it to you.
I remember that language schools like Berlitz actually have courses on cultural interaction (so that US people can negotiate with Chinese, say).
More than the phrases themselves, I think that it is important that Anglo-Americans and Germans understand each other's "different mind sets." Using the guidelines below (and similar ones) will prevent many misunderstandings.
The first thing is that any statement made by a German is "heavier," more serious and more definite than a similar statement made by an American (a Britisher is probably an intermediate case).
For instance, if an American says, "he is a good friend of mine," it means this is someone I know "pretty well" (ganz gut). If a German makes this same statement, he's saying "This is one of my top five (or so) best friends, (someone I could count on to take care of my children if anything happens to me)."
If an American says, "what don't you drop by on me the next time you're in town," it's not "insincere," but it means "why don't we try to get together?" (But there's no tragedy if we don't.) If a German says that, he means, "I definitely want us to get together because I have something I want to show you (a new house, spouse, or child, etc.) Meaning that it would be said only to a "good friend."
In general: Germans mean what they say, and the polite white lie is - if the lie is identified at all in the first place - seen as insincere.
Example: An invitation is an invitation the first time around. If you get an invitation, it is fully meant the first time, so if you turn it down to be polite, be prepared to be taken by your word and not be invited again - and you may even come across as impolite.
Any list is bound to be both incomplete and too broad.
Approach people in a friendly manner, be nice. Mention casually that you are a foreigner (not necessary if your German has an accent of some sorts). If you accidentally said something wrong, a quick apology should do the job. Remember the trap you just fell in and don’t fall into it again.
Continue like that and you will have a pleasant experience.
I am also a non-native speaker of German. One time, I have said human race (Menschenrasse) and a German friend of mine told me that I should not use this word because of its bad reputation from Hitler's time, even if this word is totally acceptable in English and other languages.
I think there are couple of words, sentences, which you should avoid using them.
Rasse.
Commented
Jun 28, 2016 at 16:40
Grammatically "Fräulein" is totally fine. But this is more about history and current culture. For us Germans (and Austrians) the word "Fräulein" is more a link to the years around 1900 and second world war. Also for the times of the upcoming bourgeoisie.
Therefore this is far in the past for us and not modern at all. This is why we avoid such "old" words.
Today being polite is more a matter of the German translation of the English "You". For instance you would never say "Du" to a person you do not know as a friend or who offered the usage of that word to you. Under such circumstances you would rather use version of "Ihnen, Ihr, Ihre", which is more polite. For instance:
German [polite]: Guten Morgen Frau Meier. Wie geht es Ihnen heute?
German [friendly, but impolite to non-friends]: Guten Morgen (Frau Meier). Wie geht es Dir heute?
English: Hello Ms Meier. How are you today?
Update: Another explanation is emancipation. Today we think as women and men being equal. But formerly a women was treated as part of her husband. Also in title. For example "Frau Magister Meier". Even though she had no academic title she was greet with her husband's title.
Anderswo auf german.stackexchange gab es die Frage, wie man "grammar nazi" übersetzt. "Grammatiknazi" gibt Ärger. "Leader" mit "Führer" übersetzen ist auch problematisch aus historischen Gründen ("Anführer" ist in Ordnung).