Alcohol is perhaps the single biggest cause of mischief world wide, without a doubt. While many people do use alcohol as an excuse to act stupid, it does not dispel the fact that alcohol does cause people to be dumber. It decreases inhibitions and slows down brain function, making people more likely to do things out of impulse.
One unfortunate result of this is the propensity for drunk individuals to think they are tough, and will be rude or talk random trash to people. Some people obviously do not liked to be talked down to or given an attitude for no reason, and a confrontation would be inevitable. Some people on alcohol will be downright aggressive.