How to politely refuse to raise the living expenses of college sons?

You can tell him reasonable living expenses, that is, you should have a sense of financial management and don't compare with others. For example, you should never save the money you spend, but learn to save it where you can spend it. Be sure to communicate with your child patiently and don't blindly refuse your child's request. After all, children should have their own ability to judge right and wrong after they go to college.