Sentence examples for should know better from inspiring English sources

The phrase "should know better" is correct and commonly used in written English.
You can use it to express disappointment or disapproval towards someone's actions, implying that they are capable of making the right decision or behaving correctly, but have failed to do so. Example: "John, you should know better than to cheat on your exams. Your actions not only reflect badly on yourself, but on our entire class."