All I can tell you is don't say the 'H' word, and don't talk about 'it' or 'him'. Really sour spot with Germany. Also, try to get a sip or two of the warm lager over there, it's really good(second only to mother vodka).
Yeah, there's a German student living in my house this year, actually, so I'm somewhat accustomed to their dislike of making jokes about Nazism and such.
I assume you've been to Germany before. Are you fluent?
well, I lived there for 3 years, then when I was 8, we moved Stateside, where I still live. Hence, I've long since lost my fluency...but I still have bits and pieces of it...and Russian