People can snap at any time. i have seen people i have known for years snap and hit someone out of anger and it had nothing to do with steroids.
I will say that i believe it is true that AAS can make an asshole, a much BIGGER asshole.
I have had a short temper my entire life and i can admit high amounts of AAS made me more irritable, but not once did i lose my cool due to "roid rage". i did snap on someone who deserved what they got, but i would have done the same if i was clean at the time anyway.
I think anyone can snap and hurt someone, but i do believe that Androgens can effect someone's attitude exponentially, specially if they are an asshole looking for trouble to begin with. Each person is different but i will be very honest and say "roid rage" is not a myth, but it is also not an absolute.
Same goes for drinking...i have seen people go absolutely apeshit after a night of heavy drinking, and they usually don't remember doing it and often do it more than once...just my .02.