Re: Social Drinking
My personal favorite:
"No thanks, I do enough stupid things sober that I can't afford to drink."
It has the benefit of being absolutely true and also getting a laugh.
Overall observation: Humor is a lubricant to just about any social situation or interaction.
"Opportunities to do good are everywhere but the darkness is where the light needs to be".
-- Eliezer Yudkowski, author of "Harry Potter and the Methods of Rationality"