Brain scans show why people get aggressive after a drink or two. Researchers have used magnetic resonance imaging (MRI) scans that measure blood flow in the brain to better understand why people often become aggressive and violent after drinking alcohol. After only two drinks, the researchers noted changes in the working of the prefrontal cortex of the brain, the part normally involved in tempering a person's levels of aggression. Source 1i.
Common sense dictates that, if you become violent or black out when you drink, you sure as heck shouldn't be drinking! Sadly, common sense isn't. Alcohol I a slow poison, with many different effects and some people are more prone to violent actions when drinking than others. It's genetics and emotional control that sometimes goes out the window when pickled.