I've never liked Rock's oversell of the Stunner...Shane gets the award for best visual when he spit out the mouthful of beer following a stunner on whatever PPV that was...
EDIT: to sell it well, I would say that, at the point of impact, the victim should pop up to their feet, briefly, jerking back at the waist and neck, arms flailing, then falling onto their back or to the side. I'd even take a slight hop into the air rather than just standing up...when the Rock does the whole fall and tumble back onto his feet and then fall again, it makes me groan...