Complete turnoff for me if a guy smoked. Not just for shallow reasons - his breath smells, his skin will look nasty, his teeth and nails will be stained etc, but I wouldn't be able to be around someone I love burning away their lungs and living in the fear that they're 25 times more likelier to get lung cancer and die. Plus there's the issue of passive smoking and the risk to me as well, but that's less important.
I know people will say but what about if your partner drinks, you're watching them give themselves liver cancer surely- yeah maybe you're right, but when I was younger I had an illness which damaged my lungs and now I have permenant scarring. So it baffles me and frustrates me when I see someone who's been given a perfectly healthy pair of lungs CHOOSING to damage them, whilst there are others who would give anything to have healthy intact lungs.