Our friends the Hehn's have a family line that goes something like "are you kidding me or just joking" that originated with one of their Ethiopian kids and an early struggle with some Americanisms in the English language. If you hang out with them you will hear it, but it is an inside joke.
When Marta first came and started to warm up to us and become playful, someone would say something to her and she would say "are you sure?" Like when a friend came over and they were looking through Jeff's yearbook. The friend pointed to the picture of herself and told Marta "that is me." Marta said, "are you sure?"
Now this has become the saying around here. Nothing like a well placed "are you sure" during dinner conversation to have everyone rolling.
Guess you had to be there...