Alcohol by far. I was what you would call a violent binge drinker. Alcohol would cause severe mood swings and depression for me. I would start fights with people and go on week long binges where i'd just drink myself silly. It's funny that i've done a lot of hard drugs but not a single one has the negative attitude changing effects alcohol has had. I had to quit drinking altogether. So it's kind of weird to my friends when I say I don't drink but then I go ahead and do everything else.