It really depends on the person and in what way ...
I think I'm too drunk to drive a car after 1 beer. It wouldn't even cross my mind to drink and drive.
But I've never been irresponsible or not clear-headed, no matter how much I drink. But I know many people who doesn't have the same control ..
It's not like I ever wished for this control, it's more like I'll get sick long before I get to the point where I'm drunk enough to do really stupid things.
As for how I would descripe my state of drunkeness to anyone who'd ask:
3 pints: Semi-sober
6 Pints: Should stop drinking about here.
9 pints: Definetly drunk.
12 pints: Shit-faced .. I'll be lucky if I'll keep my dinner.