Young men who watched TV (TV, videos, DVDs) for 20 or more hours each week were found to have a 44% lower sperm concentration compared to men who watched no TV. Those who watched the least TV and got the most moderate physical activity had the highest sperm counts. It was also noted that the physically active men tended to eat the most "prudent" diet.
PositiveTip: Don't become a reproductively challenged spud–get off the sofa and exercise moderately every day.