Question

a red rag to a bull

Accepted Answer

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 bull fighting.

1998 - Times - Such talk is like a red rag to a bull at the Soil Association. 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

Bull Red Provoke Colour Rag Object Utterance Act