Art Vandelay and BMalion:
I saw an article from some California paper that the “sideways” shooting style is becoming “old hat” with the gang crowd, because it’s too popular in the movies now. Allegedly, the new “cool” style is to hold your gun completely upside-down.
Too bad we can’t make it cool to point it at their own heads and pull the trigger! 
Okay, back on the Overdone Movie Stuff topic:
Fight scenes where the “upper hand” goes back and forth, back and forth, from Good Guy to Bad Guy, as they beat each other beyond all human endurance… often with heavy and/or sharp objects… sometimes when one has a serious wound.
That annoying rattle that movie weapons make whenever they are moved quickly. There are no loose, rattle-y bits on guns!
The whole “human is raised by animals, so he has the powers of the animal” bit.
The closely-related “human is raised by animals, so he’s smarter, wiser, more morally-developed than the rest of us” bit.
Double-barrel shotguns that make the pump-action “chunk-chunk” noise when brought into action.
The girl who stabs the psycho and leaves her knife in his chest, so he can pull it out and use it against her.
Characters who work the action on their weapons repeatedly, in order to emphasize what they’re saying. In reality, this practice simply throws perfectly good ammunition on the floor!
People who twitch once, then instantly drop dead when stabbed.
Since all psychics in movies are real, the Tarot actually works, and the tribal shaman really can see the future in a pile of chicken bones, you’d think people would begin to listen to them after decades of consistently correct prediction… but nobody does.
In movies, ALL fringe belief systems are valid (voodoo works, Native American magic works, etc.), but the immensely more popular Judeo-Christian beliefs are nearly always shown to be useless.
The “ugly girl is just an incredibly beautiful girl with glasses and a bad hairstyle” bit.
The nerd who becomes heroic and/or popular, and suddenly doesn’t need his glasses anymore.
The person (usually a woman) who puts on glasses simply to show that she’s involved in serious mental work at the moment.