When I watch a movie that has an actor handling or using guns, I watch for their trigger finger.
Is it on the trigger as they're prowling around? Or is it indexed along the side of the gun for safety, ready to access the trigger but not on it as an accident waiting to happen?
Once the finger is on the trigger, is it wrapped as far as possible around to the other side, like the hand is trying to give the gun a bear-hug?
Those actors who grip the gun funny like that, with the trigger finger curling way around the trigger, or the ones who choke-up on the back of the grip so that the web of their hand is in the way of the slide (or the hammer in the case of a revolver) crack me up.
You just KNOW that they've never used a gun in their lives, they hate guns, they don't know squat about them, and they probably made some, "Ewww!" comment when they had to take the movie prop gun in their hands.