I was approached today; "Do I know you...", with a pause followed by "...should I know you?"
It really struck me as having a profound difference in meaning.
The first line is a standard way to open the conversation in English speaking countries if you just can't quite grasp the person out of the depths of your memory. You have the feeling that you have met before, but are unable to put a name on the face. It tends to put the person being asked a bit on the defensive, especially if they don't recognize the one approaching you either.
The second is a more subtle take on the same line, putting it all in a more gentle and positive light. It puts the person being asked at ease which starts off the ensuing conversation more smoothly. It takes a certain amount of poise and style to project that something special that nudges a person into thinking that they should be able to put a name to your face.
I hope I can one day project that type of warmth to those that approach me...