Many behaviors are determined by hormones. Men are no exception. When calm, men tend to prefer intellectual women, but when they're impulsive after drinking in a bar, they prefer sexy women.
Endocrine and nervous system function take a dramatic shift when processing alcohol.
The aggressive drunks didn't get there overnight. They drink more heavily and regularly. Their nervous system is amped up even when "sober", but it takes months to years to fully recover from that state and there might even be permanent nerve damage. All this to say, they will just drink again to calm their nerves and are easily pissed off. That's alcoholism for you.
On the flip side, some of the most body aware and even keeled people I've ever known are recovered alcoholics. There's a reason alcohol has been a rite of passage for most of human history.