I'm slowly growing out of a case of social anxiety disorder, so yeah, when I was younger I was an extreme loner. Social situations scared the piss out of me. Now I'm much more relaxed and friendly, although typically I'm still quiet around new people until I've grown comfortable with them, and even then I tend to surround myself with people that will talk my ear off so I don't have to say much. Put me behind a computer screen, though, and I'm a social butterfly. To this day I'm perfectly content being alone in the house, and I'm kinda like Jersey Chick - "I like to blend in and just watch what's going on around me."
Drinking? Occassionally. Mostly in social situations, but I can't hold much alcohol. Or not much tequila, anyway.
Out of control hair? Absolutely, but I don't have a beard.
Lost in my own little world while writing? Yes... and outside of writing time, too.
Tempramental? Only when I'm interrupted in the middle of a creative streak, or during that time of the month.
Talk to myself? No. But it sort of sounds that way sometimes if I'm talking to someone on the computer through TeamSpeak. I don't think talking to myself in my head counts
Stare in anguish at the screen? Happens more than I would like, but at least I don't have a beard. Instead I resort to chewing my lip and crunching as much of myself into my little chair as humanly possible (pull my legs up, try to sit cross-legged, etc). And yeah, I
do slouch.
Stereotypes are stereotypes for a reason... they're common enough to form a familiar image in people's heads. Not everyone fits the stereotype but I bet there are more of us writer types than we think!