What is the origin of the idiom "look daggers at someone" and when to use it?

The origin of the idiom "look daggers at someone" is linked to the historical association of daggers or knives with threat and danger. In centuries past, people commonly carried daggers, which were sharp and potentially lethal weapons. The act of looking at someone with intense anger or hostility, often accompanied by sharp or piercing glares, was likened to threatening them with a metaphorical dagger or knife. It is often used in situations of conflict, disagreement, or when someone's behavior or actions are seen as unacceptable.