After a few drinks, plenty of people turn into that guy. Unless you're Russell Crowe, and then you're basically already that guy. Either way, you can thank genetics for you becoming belligerent, reckless, and overall embarrassing every time you go out drinking. And if you're Russell Crowe, those rugged good looks.
More precisely, the University of Helsinki has discovered a genetic mutation that can lead to exceptionally irrational behavior in certain people after a few alcoholic beverages. People who many would consider lightweights actually had problems with their "serotonin 2B receptor," a genetic mutation that classifies them as carriers of the "HTR2B Q20," or in other words, "The Stupid, Silly Behavioral Gene."