His method was pretty damned fast. I also noted it was pretty far down and to the middle of his glute and I seem to not recall there being any aspiration, either. It looked a little wrong to me, though I did not feel like the movie's overall treatment of steroids was at all ignorant or even really negative.
I shoot for the upper outer quadrant, but feel free to move about pretty well within that area, and I inject much more slowly now, both insertion of needle and injection of fluid, after having had some not very fun experiences occur as a result of my overzealous injection technique.
I thought The Wrestler was a pretty damned good movie, overall, anyway, and I've loved Mickey Rourke since Barfly. Certainly it is the most watchable of Aronofsky's movies. His punching that meat slicer, though...damn...yeesh. In this day of easy internet access to...well, everything, there's not much left that can make me cringe, but that scene sure as hell did.