I was once speaking to a good friend of mine here, in English.
"Do you want to go out for yakitori?"
"Go fuck yourself!"
"... switches to Japanese Have I recently done anything very major to offend you?"
"No, of course not."
"Oh, OK, I was worried. So that phrase, that's something you would only say under extreme distress when you had maximal desire to offend me, or I suppose you could use it jokingly between friends, but neither you nor I generally talk that way."
"I learned it from a movie. I thought it meant "No.""
"You might want to not repeat it ever again."
Along the same lines, I was getting a shave from a super hospitable barber last November in Gifu and the topic of conversation in very broken English (from him) and correspondingly broken Japanese (from me) was basically whether I had seen all of his favorite American movies. We were chatting and laughing quite a lot. When the time came for him to shave around the Adam's apple, he pointed right at my face and said: "You! Shut up!" It was so funny: He had obviously picked that up from a movie, but it took everything in me not to feel a little hurt, even though I knew he didn't mean to say what he said with that sort of edge. I can only imagine how many times I've done something similar in reverse. :-)