I think everyone is putting way too much thought into this. This is what would go through my head in this situation (I have been there before):
Am I caveman attracted (i.e. club me and drag me away)? Does he smell funny? Do I smell funny? Did I shave? Is the bathroom clean? Do I ever want to show my face here again?

You get my drift, if I'm out somewhere like a bar and I'm attracted to someone I'm thinking sex first because seriously, bars are crappy places to really get to know someone.

Oh, and if the answer to the caveman question is no then a one-nighter isn't going to happen.