It's not so much that sex is improved with smoking, as that smoking is so improved by sex. After all the activities and releases, smoking is much more pleasurable (as most things would be I guess) than at other times. So if you are a smoker, that's a real good time to enjoy a smoke.

Kind of like hard outdoor work is not improved by a cold beer afterwards per se, but the cold beer is improved by the effects of the work. It just tastes better then and is more appreciated then.

~S~