Good guy seemingly kills bad guy, but instead of putting a few more rounds/hits/stabs etc on the lifeless corpse to make sure, they stroll right up to inspect it and gets attacked again.
Group splitting up when there’s a killer on the loose.
Characters standing with their back against a window when there’s a killer on the loose.
Unnatural one-sided phone exposition: "He’s really dangerous you say? He’s armed you say? He’s at the old mill you say?"
Bad guy pointing a gun at good guy. *bang* *pause* Bad guy drops dead to reveal another good guy behind them with a gun.
Man and woman off screen, but you hear “that’s it, do it like that, that’s so good, right there, don’t stop!”, then the camera pans and reveals they’re doing something totally innocent.
Getting knocked unconscious by innocuous things. Groups of people regaining consciousness simultaneously.