red rag

• Shortened from red rag to a bull

red rag (plural red rags)

1. Something that will enrage another particular person.
   • 2008, Sep 24, by Lindesay Irvine in guardian.co.uk, Collins, we're lost for words: let's call your bluff,

     Collins dictionaries has announced that the inclusion of 2,000 new words in its forthcoming new edition means that some of the dustier corners of its lexicon will have to be swept into the semantic dustbin. Farewell embranglement, recrement, fusby and numerous others. This will be a red rag to books bloggers everywhere.

• Drager, Gerard, Grader, grader, regard