All the above answers are true. I might add that how many years a person has been drinking and what has happened during that time can also be a factor. For example in my 20's and 30's I could drink til the cows came home with no change in thoughts or behavior whatsoever. Now in my mid 40's, I gotta be more careful with it. It's funny that the war on substance abuse is funded by alcohol and tobacco tax revenue, so does the man really care what substance your using, or rather WHO'S substance? Just a thought.
I think ts is because drinking amplafies how they are feelings. So if some one is sad, when they drink, they may become a bit sadder, if they dislike a person, they may become mean and agressive towars that person. But if theya re in a good mood they should continue to stay in that good mood, untill the hange over hits that is.
It can vary on what their drinking and how they were feeling before drinking. I get mean when I drink whiskey for some reason and not when I drink anything else. If i'm in a bad mood before drinking I can become a depressed drunk. It all varies on how you were feeling and what your drinking.
Becasue we all have different personalities we all react to different things in diferent ways. You could also ask why some people are violent and others arent, no one is the same and when under the influence of alcohol we all react in different ways.
I don't believe alcohol does something mysterious to people. People who are mean drunks, aren't exactly great people when they're sober. Alcohol simply lowers inhibition. It doesn't make someone turn into something they're not.
I think it depends on what has happened in their past and how they have brought up. I find that mean drunks are often the saddest people underneath the meanness and they need to most help of all the drunks.
It all depends on your mood and hormones. And what type of drink your drinking.