"You have an American accent!"
It was not said with any sort of hostility; rather, it was said with enthusiastic surprise, as the person expected me to speak with a much stronger British accent. I thanked them in a tone that clearly displayed my pleasure at their statement.
I know I do have a British accent, but it's not that strong and, unsurprisingly, I frequently speak in American English and use American terms despite writing in British English. I consider it a compliment when someone notices that my accent is different; I was having a fairly miserable day until that moment.