There’s alot of great advice here, especially around empathy and therapy. I would also say try to check in with yourself when you get stuck on frustration over the exterior; for instance, as some said nicotine addiction can be a cause, anger can also be caused by physical (hunger) or mental cues (anxiety/overthinking over “wasted time” etc.). Also, alot of times anger or frustration stems from an idealistic view on life; like getting annoying at traffic when you know it’s normal for traffic during the rush hour etc