Son of Liberty
The mans got a point...that'd definately scare me out of it.
to be honest it'd scare the bejeesus out of me to... but then again you have to take into consideration that most users of Steroids are much akin to those who are Bulimic or Anorexic... They feel that their bodies are not "up to par" and so they take these extreme measures, sacrificing their own health, disregarding the actual effects of what they are doing in order to alter their body.
I do believe that if he is that concerned with pumping up, that he wouldn't care if his junk took a sacrifice, just as long as his muscles keep growing. Hell he might even find a way to convince himself that this particular side effect is nothing more than a joke.
This is why I feel the scare tactics of trying to show him these side effects are not going to be useful. You've got to treat it like he's suffering a disorder... because that's exactly what it is. He's obsessed with achieving this body that he'll stop at nothing. So the only way to actually get to him is through his heart & mind.