What does this cold joke mean? .

In other words, the speaker will always laugh, and the listener will generally feel speechless. Even though he was laughing all the time, he would wonder why I laughed when I heard this joke: I had a friend named Cai Xiao, and in a few days, he was taken away by others. I couldn't stop laughing when I first heard this joke, but now I want to know why I laughed at that time.