Script (guión): Idioms, ‘red rag to a bull’. If something is a red rag to a bull, then it is something that will inevitably make someone angry or cross. For example, my cousin is quite overweight, quite fat. He doesn't stop eating and if you say the word porky in front of him, he goes completely crazy, smashes things, gets violent and could attack you quite easily. Actually come to think of it I hope he doesn't see this video or I'm in trouble.