I love to drink alone, especially at bars. With regards to getting really drunk, which I sometimes do, I never really talk to other people at the bar unless spoken to, and even then I try to keep conversations short. They might be able to tell I'm drunk if I DO something stupid, like walk into a wall or drop some change and laugh heartily.
Mostly I just love observing people, in a melancholy sort of way. I'm not really much of an extrovert and am kind of socially retarded but the world don't seem so bad when your perception is soaked in awesome. And, walking/biking home at night while drunk and listening to music is one of the best experiences ever.
My gf has a problem with it though, as she's pretty much the complete opposite me, quite the social butterfly, optimistic and loves to party, etc. She thinks it's quite lonerish to drink on one's own, and thinks it's unhealthy and even vain. Sometimes I wonder why she even likes me, but I guess I can't really complain.