Watched the Fellowship Of The Ring last night - the amount of times Pip and Merry got them into deadly danger out of stupidity turned me puce (just my face). Would have grabbed them by their hairy ankles and dashed their brains out against the nearest ent.
Obligatory ring gag:

Douchebag characters who completely lose their sht in the middle of a bad situation.
Drives me nuts and then I turn into a douchebag character yelling at those douchebag characters. It's fckn crazy homes..
http://www.imdb.com/list/ls066138215/

porno for pervs
Dude, the band is called Porno for Pyros. Get it right.
You got the wrong guy, mang. I don't come off no banana boat.

I LOVE sex, lots of it, but other than porno for pervs, no sex scenes please. Yes, show some boobies and front and rear (females preferred) but stop with all that smooching, and slow, over-dramatic, taking-your-sweet-a$$-time-before-going-at-it, blah, blah. It's so annoying on film.
Complete October challenge -
http://www.imdb.com/list/ls066581682/

Ones that get straight into the action without any buildup and/or are nothing but action the whole time. It makes me think "I don't know these people, so why should I care what happens to them?" I think it's very important to let us know what the character's lives are like normally before all the horror begins and let us get to know them through how they react in situations.
Also ones with loudmouthed, obnoxious characters. This has seemed to be more of a problem in newer movies. You can be funny and sarcastic without being over-the-top and annoying.

American curse words peppering the dialogue, particularly in films featuring a group of young "adults."
I am so fckn sick of it that I literally can't continue watching the fckn movie once it starts. Seriously.
Pardon my French.

I dislike volume raises too to get a scare out of people. It's rather cheap to score but it seems to work on the jump scare lovers.

Sound design is really important in a film for me. Films these days tend to over use sound to the point where it's so over the top with an unwarranted exceptionally loud volume and that pisses me off. I really enjoyed The Possession of Michael King but there's moments where the sound is just ridiculous and jolts you out of the film.

Obvious CGI

Boring sh!t.
Such a buzzkill right there.
You got the wrong guy, mang. I don't come off no banana boat.

Overly moralizing. Movies that are quite explicitly from scene 1 trying to express some kind of moral lesson that subtracts from my entertainment.
"A Girl Wants Romeo, Not Hamlet "
-Blair Waldorf

Bratty kids. Nothing kills a movie faster than bratty kids.
Excessive swearing. It seldom feels organic to the characters, especially if every character is doing it. It takes me out of the picture, feels like what it is: an artificial attempt to seem edgy or secure an R rating.

One common weakness in horror movies is dialogue that's all Question & Answer. Sometimes it's not even useful for exposition, and always leaves the actors treading water as the pace comes to a halt.
Certainly not the worst, but my most recent experience was with The Neon Demon - it kinda grinds my teeth.