When someone suffers no hearing loss after firing a gun (or guns). This even made it into Ebert's Movie Glossary book:
Movie heroes squeeze off hundreds of rounds of ammo but suffer no hearing loss. For example, RAMBO II, where Rambo enters a metal warehouse and runs an entire belt of ammo through his M-60 machine gun. Afterwards he carries on a whispered conversation with the evil CIA man in another room.
In fact, in most movies where guns are fired, especially by a character who is supposed to have no gun experience, there always seems to be very little recoil at all. Unless it's crucial to the plot or scene.