Answer:
In effect it has been widely rumored that energy drinks or Mountain Dew (mainly the additive Yellow Dye No.5) can cause:
Sperm Sterility
Penis Shrinkage
Testicular Shrinkage
Some sort of genital cancer
and etc...
Oddly enough the high contents of Taurine, Guanine, Caffeine, and various other hard to pronounce chemical compounds have not proven conclusively that this is true. In fact in certain studies caffeine has been found to correlate with catalyzing sperm mobility (making your boys swim faster). As in any other products, moderation will usually ensure less likelihood of uncommon side effects so don't go nuts.
The only studies to show a negative effect are related to heart health and obesity/diabetes related articles.