a red rag to a bull

a red rag to a bull

A willfully infuriating or aggravating provocation; something that incites great anger or annoyance. An allusion to matadors' practice of waving red flags at a bull during a bullfight, though the color of the flag actually makes no difference to the animal. John's gone to gloat about his success over his brother, which is a red rag to a bull if I've ever seen one. You do realize that bringing your new girlfriend to your ex-wife's house is like a red rag to a bull, right?
See also: bull, rag, red
Farlex Dictionary of Idioms.

a red rag to a bull

BRITISH or

a red flag before a bull

AMERICAN
If something always makes a particular person very angry, you can say that it is like a red rag to a bull or a red flag before a bull. This sort of information is like a red rag to a bull for the tobacco companies but it really needs to be exposed. It's a red rag to a bull when my son won't admit that he's wrong. Compare with a red flag.
See also: bull, rag, red
Collins COBUILD Idioms Dictionary, 3rd ed.

(like) a red rag to a bull

an object, utterance, or act which is certain to provoke or anger someone.
The colour red was traditionally supposed to provoke a bull, and is the colour of the cape used by matadors in bullfighting.
1998 Times Such talk is like a red rag to a bull at the Soil Association.
See also: bull, rag, red
Farlex Partner Idioms Dictionary

(like) a red rag to a ˈbull

(British English) (American English like waving a red flag in front of/at a ˈbull) certain to make a particular person very angry or even violent: Don’t mention anything about religion to your uncle. It’s like a red rag to a bull.
This expression refers to the belief that bulls do not like the colour red.
See also: bull, rag, red
Farlex Partner Idioms Dictionary
See also:
  • a red flag to a bull
  • be like a red flag to a bull
  • be like a red rag to a bull
  • close (one's) ears to (someone or something)
  • a security blanket
  • shut (one's) ears to (someone or something)
  • shut/close your ears to somebody/something
  • get (something) into (one's) thick head