Probably the least common surname is mine. My surname is Ping, Ping Ping. When many people get to know me, they think I am joking with them, because they have never had it since they were little. I've heard of such a surname. But when I told him it was true, they were surprised because when I first met him when I was a child, this surname is probably only found in Heilongjiang, and there are very few people with the surname Ping. The only people I know who have the surname Ping are my relatives, and I have never been in contact with anyone else. And I have also looked for this surname in the Hundred Family Surnames, but I can't seem to find it.
I also have a primary school classmate whose surname is Hao. I was very surprised at the time. He introduced himself to us as Hao Xin. At that time, we all thought he was joking until I worked with him for two years. Only then did the classmates find out that his real name was Hao Xin. From elementary school to now when I graduate from college, I have heard of only one named Hao, and he is the only one.
I also had a high school classmate whose surname was Shi. At that time, we all laughed at him because of his surname. I have never seen this surname again after I went to college.