Green poop is generally the result of either too much iron, or too much food coloring.
Have you recently eaten a lot of colorful cereal, frosted treats, or anything else clearly dyed in excess? If so, then what you're seeing is your body basically crapping those colors out.
Have you recently started taking a supplement or vitamin with iron? If so, then stop immediately. Unless ordered to do so by a doctor, men should never take iron.