I do think it's different for everyone -- the definition, I mean. I had a friend at university who claimed that there didn't need to be penalties for drunk driving, just reckless driving, because he was a perfectly safe driver when drunk. I was all "..." because WHAT.

My maternal grandfather's rule was that you never drink sitting down, because you'll think you're sober far longer than you are, and by the time you stand up it's too late. My rule is that if my lips get numb, it's time to switch to water until I can feel them again, and I have to have been able to feel them for an hour before I will drive. (It is rules like this that keep Keith Richards alive, people! I have heard that Keith has a rule: he will buy a certain amount of drugs for his bender, and when the drugs are gone, the drugs are gone. No buying more drugs until sobered up. Well, he's still alive.....)