What does the old saying I'll brain you both mean?

The old saying "I'll brain you both" typically means to threaten or warn someone that you will hit them on the head, often implying a serious consequence for their actions. It suggests a level of frustration or anger towards two individuals and is used to convey a sense of authority or power. The phrase is often used in a humorous or exaggerated context to emphasize the speaker's intention to discipline or control a situation.