Cars exploding just by being shot at (can only happen if you shoot them in the gas tank IIRC, and even then only with incendiary rounds, since whatever the gas tanks are made of is designed NOT to make a spark from anything hitting it, whereas incendiary rounds have their own fire)

Lack of flight response (like Thorn said. Yeah, let's just walk towards this scary sound when there's some killer whatever on the loose)

People can't hit for shit (if you're supposed to be this soldier/hitman/what-the hell-ever, it's implied YOU CAN SHOOT STRAIGHT)

Dying mid-sentence (can happen, but damn it's overused)

Bad guy delivering a damn monologue and then dying because he was too busy talking (if you're gonna kill someone, just do it, dumbass)

Someone looks inside a really dark room, gets complacent and just turns around to head back, and then something grabs them from behind and drags them inside the room (it's like, if there's a damn killer alien or monster or whatever on the damn loose, don't turn your damn back on the damn dark room until you're damn well away from the damn room. You take quick damn looks behind you to make sure you damn well know where you're going, but if you know for damn sure the way behind you is damn clear, keep your damn eyes forward, damnit)

And various others i can't think of right now.

EDIT: Tripping over and then not getting back up, instead opting to crawl around (IT TAKES ALL OF A SECOND TO GET YOUR ASS BACK UP)

EDIT: Yeah, pretty much http://cinemassacre.com/2010/01/20/t...movie-cliches/ that.