From Longman Dictionary of Contemporary Englishlike a red rag to a bulllike a red rag to a bullBritish English (also like waving a red flag in front of a bull American English)ANGRYUPSET very likely to make someone angry or upset Just mentioning his ex-wife’s name was like a red rag to a bull. → red
Examples from the Corpus
like a red rag to a bull• Naturally this was like a red rag to a bull and I refused to even consider such a course of action. 