My German teammate has had a tough time adjusting to our American English! Here are a few examples:
While it's a sign of hospitality in English, in German it's more of a put-down, like we might say, "Why don't you get it YOURSELF?!"
What's that? (with a rising tone)
We say it to mean, "I didn't hear you. Could you repeat that?" but she understands it literally, meaning we didn't understand one of the words in the sentence and need an explanation.
These days, it's slang for "No way!" "Wow!" or "You're kidding me!" and is meant in a positive way, but my German friend hears it as a rude command.
You can imagine what she felt like her first few days here, if the dialogue went something like this:
Rahel: Thank you for letting me stay at your house.
Karis: No problem! If you need anything just ask me, and feel free to HELP YOURSELF!
(Rahel thinks I hate her)
Rahel: I finally got that phone call I was waiting for!
Brittany: SHUT UP!
(Rahel thinks Brittany hates her)
Rahel: Sawatdee kha. ("Hello" in Thai.)
Mark: WHAT'S THAT?
(Rahel thinks, Hmmm... he's been in Thailand for 5 years and still doesn't know the common greeting??)
My friend had to hide in her room for a few days (just kidding!) but we now have some pretty good inside jokes.