red rag to a bull

The phrase "red rag to a bull" is an idiomatic expression used to describe a situation or action that is likely to provoke a strong and aggressive reaction from someone. It originates from the behavior of bulls, who are known to become agitated and aggressive when they see the color red. Therefore, something that acts as a "red rag to a bull" is a trigger or provocation that easily angers or incites someone.