When is enough enough?

I've just been out for the department Christmas do. I walked into the house and Dave said "you're pissed". Thanks Dave, I thought, but I can still walk and talk - that's good for me.

But it made me think. What is it that tells me to stop drinking? and I decided that my feedback loop isn't particularly well developed.

I tend to rely in my senses. And when they start to fail I stop drinking. That's probably too late.

Any advice?