Smoking
Credit: Getty Images

Turns out lighting up is not nearly as sexy as it's made out to be. Smoking not only messes with your sperm, it can also cause narrowing of the arteries. Bad arteries likely means bad blood flow to you-know-where. This is no small effect either. Research has found that men who smoke are twice as likely as non-smokers to develop erectile dysfunction. Even worse, the damage that smoking does to blood vessels — and the effect that has on sexual functioning — can be permanent.