This is not often used.
Xi Xi m: n
Barefoot, no shoes and socks: trip. Tilt (expose the instep)
If you are right, the source is not Cao Cao and Xu You.
This is an allusion to greeting each other with upside-down shoes:
When the Emperor was offered in the Eastern Han Dynasty, Cai Yong, the left corps commander, was a well-read writer and calligrapher. He was highly valued by the imperial court and was very famous at that time. He often stays at home for weddings. One day, Cai Yong recited the Book of Songs with several guests at home. A servant announced that RoyceWong was visiting. Cai Yong couldn't wait to rush out, even wearing his shoes backwards. With great courtesy, Cai Yong welcomed RoyceWong in very politely. At that time, all the guests were surprised at what characters would make Cai Yong so anxious. It turned out to be a young and thin child, which surprised everyone present. Cai Yong said, "This is Prince Wang Fu. He has a unique talent. I feel sorry for myself. All the books and articles in my family should be handed down by him. " RoyceWong is really a man of super intelligence, it's all right to ask. He can read silently, recite backwards, arrange the messy chess games exactly the same, and write articles and poems very well. Later, he became a famous writer in the late Eastern Han Dynasty.