When two people meet, and one of them says hello but the other one can't recognize him or her, the other one would ask "Do I know you?"
I know this is natural for English speakers but it could be strange for some non native speakers like me.
Because in this situation I would ask "Do you know me?"
Why do English speakers ask in this way?
From a common-sense standpoint, it is strange to ask others whether I know someone or not.
Best Answer
"Do I know you?" is an idiomatic expression that could be used when you can't recognize a stranger who says "Hi!" to you. Depending on tone and intonation, it could be interpreted as cold rejection uttered to avoid him/her or friendly gesture to ask him/her to elaborate on where/when/how they met before.
"Do you know me?" could sound more rude and cold than "Do I know you?".
There are other English expressions using this construction, for example:
It asks others to tell the questioner what happened while (s)he was absent. Using your explanation, the question sounds weird because it asks others whether I missed something or not.