I'm going to go with the "amplifies whatever you're feeling" I can be a happy drunk, but the minute any tiny thing goes wrong, I get extremely angry or extremely emo.
Not sure if I ever told the story on here, but on the way to Snakes on a Plane, a few friends and I were drinking and Die Hard came up. My friends were like, "It's not that good" All of them agreed. I got very pissed off. When we got to the theater, I threw a full Heineken keg can to the ground in disgust and was yelling loud as hell in the parking lot. I was yelling and was pissed off for probably a good 10 minutes. Two of my friends actually left.
...I stopped drinking for a while after that.