Warning - this story is borrowed from my lovely friend Esther.
In boutique handbag shop in the World Financial Centre:
Sales girl: "I make some of these bags myself you know".
Esther: "Oh, they're great, I really like them".
Sales girl: "I love your accent, where are you from?"
Esther: "Australia, I live in Sydney".
Sales girl: "Wow, your English is amazing!"
Esther (puzzled but not wanting to embarrass the girl): "Thank you ..."
Sales girl: "So what language do you speak in Australia?"
Esther (as the next customer in line giggles): "Err ... English ..."
I better go and submit this on http://www.overheardinnework.com now!