Don’t stick your chopsticks into your rice.
I was having dinner with my family back in my father’s home town when I was younger. When we are watiting for other family members to be seated, my younger cousin casually sticked his chopsticks into his bowl of rice. My father stopped him. My father told me that it is not right to stick your chopsticks into rice because people only do that when they are worshipping ancestors or in front of a grave. Doing so on a dinner table is extremely rude to others and also brings bad luck to people. Basically, you would only stick a pair of chopsticks into rice in front of dead people.
The story was told on a dinner table to stop my counsin’s impolite behavior. It happened during a family dinner with other members in my family.
There are a lot of different manners you are supposed to follow on a Chinese dinner table. I shared the same experience as sticking my chopsticks into rice and got shouted at by my parents when I was younger. A kid may just do it because of fun or childish curiousness, grown-up adults should tell them not to do so by explaining the culture to them gentally.