red rag to a bull

• Possibly refers to the red cape used by matadors in bullfighting.

red rag to a bull (plural red rags to a bull or red rags to bulls)

1. Something that will enrage another particular person.

   Simply mentioning the word "nationalism" to him is like a red rag to a bull.

   • 28 March 2023, Graeme McGarry, “Scott McTominay earns place in history as Scotland stun Spain”, in The Herald‎:

     The rolling around and screams of anguish from Porro though were like a red rag to a bull for the Scotland support, who howled and harangued his every touch before he was withdrawn at the interval, presumably for his own safety.

• This is often used in constructions equivalent to make someone see red.
• This is often shortened to red rag
• This is often used as a simile with like a or as a