For those that don't know, I'll describe some of the things that your body goes through when having an orgasm (from a male perspective), and why smoking a cigarette after them seems to introduce a whole different level of pleasure. During orgasm, it feels like nearly every muscle in your body is flexing, or stretching. Sort of like how you feel when you wake up in the morning and stretch in the sun. You feel a wave of pleasure rippling through your body, particularly concentrated around your groin, although during a particularly intense orgasm you may have other areas that also feel amazing.
The culmination of this is the well known male eruption, which results in a salty fluid being ejaculated. Directly after this ejaculation you feel totally relaxed, accepted and calm. You feel at peace in the world, you are totally warm; almost as though you were back in the womb. Now is the perfect time to look into your partner's eyes and light them (and you) a cigarette. The rush of nicotine into your blood stimulates your body and cuts off the circulation of blood to your brain. Your heart rate increases slightly and you feel a slight buzz.
Due to the fact that your heart is pumping blood through your body a little faster, you will probably find that you start to find your desire for your partner returning, even though you have just satiated that desire. Interestingly, it is through an excessive flow of blood that the penis becomes stiff. The cigarette will relax your mind even further than it already is. During sex, chemicals called endorphins are released which relax your body and cause pleasure, so you are probably already very relaxed.
Also, the moment after orgasm is, for males, the most contemplative moment on earth. It is a moment when you need to lie back quietly and reflect on life's mysteries, your love for your partner and your general happiness. Fitting in with this, the act of smoking a cigarette is also a contemplative moment. You breathe in the smoke, puff it out and look at the spirals of smoke head towards the ceiling, thinking calm and relaxed thoughts.
In my opinion, everyone should try smoking a cigarette after having an orgasm at least once, but you should beware of getting addicted to smoking, because it causes fatal lung disease. Personally, I don't smoke any more, although I'd share one with the late Bill Hicks if he was alive.