This is the one I find most annoying:

KER-CHAK! We’ve all seen this one. The good or bad guy had been holding a shotgun on his opposite number for a while and, just for dramatic emphasis, racks back the pump to chamber a shell. Loud Ker-Chak! Then a take-away line. “Be sure to say ‘hi’ to your mama when you get to Hell!” This is very cool and dramatic and I do love that sound effect. But what this actually means is that the character has been threatening everyone with a gun that has no chambered round. If he pulled the trigger nothing would happen.

GGGaaarrhhh, I can’t stand seeing that in a movie.

More mistakes here.

Hat Tip: SayUncle