Its a bull term people came up with ignorantly is response to the additional test driven aggression often experienced. They even made a movie with Ben Afflect (of all people) about roid rage ruining peoples lives?
The documentary Bigger, Faster, Stronger gave some statistics on it. I can't remember the numbers but basically it's non-existant. We all experience mood swings for one reason or another regardless of any supplementation. Basically it comes down to "control your hormones."