Legit: Any kind of testosterone supplementation including anabolic steroids -- the kind used by athletes and the insanely vain -- can decrease testicular function and thus dramatically reduce fertility. (For more details, See Dr. Ken's article on the effects of steroids.)
Kevin Winter, ACMA / Getty Images
Drinking Mountain Dew
Bogus: Doing the 'Dew won't affect your sperm count in any way. There have been rumors about other soft drinks, as well, and these are also incorrect. (Decreasing soda intake is worth considering given the empty calories and potentially harmful chemicals the drinks often contain.)
Joe Raedle, Getty Images
Bogus: Shooting blanks is not likely to occur as a result of coffee, tea, or even No-Doz. Excessive intake may have very slight effects but are not likely to effectively impact fertility, so your cup of morning of coffee won't have any meaningful impact.
Earl S. Cryer, AFP / Getty Images
Legit: Chronic and frequent marijuana use impairs sperm and lowers sperm count. It also lowers testosterone levels, which can lead to impotence, loss of interest in sex, and gynecomastia, aka "man boobs."
Bogus: Masturbation will not cause infertility or, for that matter, blindness or hairy palms. If it did, the human race would have died out long ago.
Bonnie Biess, Asylum.com
Bogus: The normal range of testicular size is quite wide and all sizes, even though small-ish ones, will produce plenty of sperm. If you have concerns about your size, ask your doctor and he/she can assess if there is a problem.
Legit: Sitting on an un-ergonomically shaped bicycle seats for prolonged periods can do two things. 1) It can raise your scrotal temperature and which can decrease sperm production. 2) It can damage to the blood vessels that carry blood (i.e. nutrients) to the testicles. Softer seats and taking breaks can help you avoid this.
Paul White, AP
Regularly placing a laptop on your lap
Legit: If you keep a laptop in your lap, the heat emitted can increase the temperature of the testicles and may consequently decrease sperm production. Keep the laptop on the desk or use a laptop board or pillow to create a buffer in between the computer and you.
Keeping a cell phone in your front pocket
Legit: It has been repeatedly demonstrated that cell phone exposure can harm sperm function. In general, the further away from you keep the cell phone, the better. (See Dr. Ken's article on the harmful effects of cell phones for more on the risks and ways to protect yourself.)
Yoshikazu Tsuno, AFP / Getty Images
Wearing tighty whities
Sort of Legit: There is no actual data showing this to be true, but since anything that raises the temperature of the testicles can potentially impair sperm production tight jockey shorts could, theoretically, do that. Not worth getting crazy about, but if you're trying to have kids, boxers might be a better bet.
20th Century FOX / ZUMA Press