A red rag to a bull
Definition 1 of 1
Pro Tip 1/3Anger Cue
Use it to describe actions or words that will certainly make someone angry. 
Telling John he's wrong is like a red rag to a bull.
Pro Tip 2/3Intensity
It implies a strong, almost uncontrollable reaction, not just mild annoyance. 
Mentioning the rival team's victory to him was like a red rag to a bull.
Pro Tip 3/3Cultural Origin
Originates from bullfighting where a matador provokes a bull with a red cloth. 
Discussing politics at the dinner table is like a red rag to a bull in our family.