The idiom like a red flag to a bull means something that makes a person react with sudden anger or excitement. It describes a situation where a small action or comment quickly sets someone off.
The expression comes from bullfighting, where a matador waves a red cape to attract the bull's attention and provoke it to charge.
The expression comes from bullfighting, where a matador waves a red cape to attract the bull's attention and provoke it to charge.
Teasing my brother about his team losing that game is like a red flag to a bull.