Don't be too polite when others go home. what can I say?

You can reply like this: OK, I won't be so polite in the future. I see, but I don't want to use words to show that you and I have a sense of boundaries. Remember that everyone loves face and save more face for each other. Even if there is something wrong with the other person's understanding ability or work habits, you should reserve your opinions and just talk about it. Don't judge too much and save face for the other person.