I think it would make a person more reckless, and that could lead to behavior that would seem to be or actually was aggressive, especially if you were inclined that way already.
I think recklessness was the effect of THC on Michael Brown.
The effect of THC was an issue at the grand jury. From what I've read, the state took the position that the THC contributed to his aggressiveness, while the Brown family's pathologist Michael Baden testified that he didn't think it would've had that effect.
Heavy users begin to experience paranoia which would explain instances of aggression. As far as driving stoned, it’s not a good idea. The actual act of driving itself isn’t so much the problem, since the fear of being stopped is enhanced. The problem is distractibility, fiddling with the music, talking, anything other than concentrating on driving. I can imagine crashes are more likely due to this distractibility. So many distractions behind the wheel nowadays.