Why is drinking water in class disrespectful to teachers?

The reason can be traced back to thousands of years ago. In ancient times, there was a teacher who thought he was excellent, and all the students he happened to teach later became outstanding people. One day, he gave a speech in class. In order to get rid of a particularly stupid student in the class, he pretended to be "rotten" after seeing his students drinking water: you don't respect the teacher! Get out!

So later people thought that drinking water in class was disrespectful to teachers. ........................