There was a book (I think The Intelligence of Emotions, or something along those lines) that says that we get angry when a boundary (be it a physical, emotional, ideological boundary) has been violated. Sometimes these boundaries have been set unintentionally in an irrational way (such as a childhood trauma, or as a defense mechanism to rejection or something else "bad" that might happen). It's good to investigate your triggers and consider if they are actually rational. Sometimes it can be. It can be very hard to look at and adjust. Nigh impossible in the moment.