Xiao Z's smirk

Xiao Z often smirks, no matter what the occasion, he can laugh and export, and even he can't tell why he laughs. In other words, he is simply not serious.
Xiao Z often laughed when he was quiet at school or when he was quiet. When he was very quiet, it made the class messy. After a night of self-study, everyone was very quiet to do homework or read a book. "Ha ha ha ha..." Suddenly a very loud laugh came from behind me. I turned around and Xiao Z was laughing. However, nothing funny, why did he laugh? I really can't understand.
"Haha..." Several girls were infected by his laughter and began to laugh. In the front row, there are several boys who are afraid of chaos in the world. "Quiet!!!" I shouted at the same table. However, Xiao Z smiled even more, until the class teacher came to be quiet.
Xiao Z’s laughter is often a smirk. When he smiles, his body leans back, his mouth is wide, his eyes are almost big, and his eyes are almost a seam. "XXX, sit down, ha..." Xiao Z is the length of my desk, look, I don't know why, he always laughs when he is serious, and he doesn't know what to laugh at.
Because of the small Z old fight, the class teacher Wen told him to go to the door to talk. Because I was sitting by the window, I almost heard something. "You said that you are fighting, what should I do?" "Mr. Wen, hehe..." Most of the faintly heard of me was his laughter. I really don't know how he can laugh.
The little Z who always loves to smirk is really difficult for the class committee. His face is also thick. He will only smirk no matter what he says to him. If he is too much, he will go up and play a word or swear.
Ugh! There is a small Z in the class that is really interesting!