What does he mean by "out of line"?

Native speaker’s answer
Rebecca
To "be/step/act out of line" means to act or behave in a way that is breaking the rules, or in a way that is unacceptable or improper. For example, swearing at someone for no reason would be considered "acting out of line." Ex: Your comments were out of line. Ex: My son's teacher told me that he was acting out of line in class today. Ex: You stepped out of line today. I'd like an apology.