Wilhelm scream. Please get rid of it.
This.
It's everywhere. Something explodes, someone falls, someone sneezes....
I'm sure they intentionally try to work it in somewhere, somehow.
There's also a glass-break sound somewhere too that I've heard several times, like some kind of ceramic urn shattering. I first had it firmly imprinted into my mind during one of the Red Letter Media movie reviews, and I've since heard it in several movies and TV shows. It's the Wilhelm Scream of glass breaking.
Oh, here's another one: Heroes in battle never wear helmets, yet never get killed by blows to the head. They do this so that the audience knows where to look, but it makes no "realistic" sense.
Related to helmets: Spacesuit helmets. They're made so you can see the actor's face. Lots of internal lighting, no tinting, lots of room to move around in (or to allow aliens the ability maneuver themselves into available orifices), and always made of glass from the 1600s that would shatter under the stress of a space slug crawling across it at a leisurely pace.
Lack of peripheral vision.
I dislike it when Hollywood shows someone sneaking up behind another person when in fact the main character is in an open room and would see someone coming a mile away, but because the villan is off camera, the main character has no peripheral vision. Just trying to sneak out of my daughter's room when she is falling asleep and not making a sound makes me realize how hard it would be when the hero expects it to happen.
MST3K had fun with that.
"Let's go this way, even though I see them running that way!"
"I
refuse to look to the right. It would be caving in to look that way, so I won't."
Related: Maybe it's just me, with respect to sensing other people around you: The ability to sense when someone's walking behind you by feeling the vibrations made in the floor, or hearing the slight change in any ambient noise that's caused by their occlusion or absorption of sound.
When there is a gunfight, and the hero or heroes fully jump out of cover, exposing themselves clearly before they start firing. This bugs me to no end; especially when the opponents are firing thousands of rounds that can't seem to hit a guy that is completely in the open.
See the latest Resident Evil for blatant overuse of this mechanic.
Addon: Anything more resilient than aluminum foil is capable of stopping any bullet, unless it's convenient to the plot to have it fly right through.
Except for windows. You can always shoot through them.
Well, usually.