Impotence is 50% more common among male smokers than non-smokers.
Two things have to happen for a man to get an erection. Blood has to flow into the arteries of the penis, and then has to stay there.
By smoking these processes are impaired. Firstly, smoking hinders the supply of blood from reaching the penis in the first place, because of fatty deposits in the arteries. Then the high concentration of nicotine causes the brain to send out signals that stop the valves in the blood vessels closing properly to trap the blood in the penis. Putting it simply, smoking leads to less blood getting into the penis, which is then less able to stay there.
So keep 'up' the good work boys!
(bad pun I know )