For me…old movie stunts that obviously didn’t have a lot of thought beyond “You’ll be fine. ROLLEM!!”
I don’t mean old old old stunts like Keaton. Those are supposed to make your jaw drop. But just little things. I can’t really think of any examples right now, but I definitely remember seeing some. I guess ones like Eli Wallach nearly getting his head sheared off by a train in The Good the Bad and the Ugly. Though in that case, I heard about it before seeing it.
Like Tom Hardy hanging from the vehicle in Mad Max Fury Road?
Or most of Fury Road.
Here it is without the digital effects. It’s almost more intense when you see what was real.
A cameo by a famous face will do it for me.
Example: in the not-that-good Jackie Chan version of Around the World in 80 Days they suddenly come across a Turkish Sultan played by Arnold Schwarzenegger. Or, in the highly enjoyable film Stardust, the pilot of the dirigible is Robert DeNiro (who is, for some reason, a very campy gay character).
The Wilhelm Scream.
Continuity errors, and production artifacts (like microphone heads) that wind up in the shot.
My continuity error example: the Paul Newman movie Nobody’s Fool. In that film, it’s winter, and Newman plays a snowplow driver. There’s a scene with him and Melanie Griffith, as he’s preparing to head out of the house. As Newman delivers a line, he puts on one glove, then the other. There’s a cut to a shot of Griffith as she delivers her line, then it cuts back to Newman…who delivers his next line as he puts on one glove, then then other. :smack:
When I first watched the film, probably on VHS, I stopped the tape. “Did I just see what I thought I saw?” I felt compelled to rewind, and watch again, just to make sure. 
Almost anything with trained dogs. They bark on cue looking happily expectant for the reward, when they are supposed to be barking threateningly; in a touching reunion scene they allow the boy to pet them while looking at their handler off screen.
Horses are even worse. Nobody gallops their horses everywhere unless they want them to drop down dead. Covering distance in a hurry is accomplished mainly at a trot, an uncomfortable uncinematic gait, unless you’ve got relay horses waiting in a few miles (like the Pony Express). If you are spending days in the saddle going someplace you will be almost entirely walking.
One that always bugs me is when there’s a car chase scene and you can see the skid marks on the asphalt from rehearsals or previous takes. I imagine it’s hard (if even possible) to clean the rubber off the road, but I always wondered if maybe they could do the practice runs a hundred feet away.
For the life of me, I can’t find it online, but a few days ago I was watching Smokey and the Bandit and noticed a good example of it. When he saw Sally Field in the middle of the road he locked up his wheels and skidded to a stop (or made a u-turn, or peeled out, I don’t remember) and you could see 5 or 6 other sets of skid marks.
This. I’ve never understood what the big deal is, and more specifically, why the trivia section of IMDB has to point out exactly when it is used in a movie.
Fifty-star US flags in anything set before 1959. Larry Hagman had one in his office in The Eagle Has Landed, and all of a sudden I wasn’t in World War II any more. (Even worse, but on TV and not in a movie, there was one in Margot Kidder’s bar in the James Garner series Nichols, set around 1914.)
Anachronistic technology, like a young George Patton riding an M3 Stuart 40 years before they were developed. Also, things like Shermans being substituted for Panthers with only a coat of paint used to disguise them.
Actors doing either bad or totally inappropriate accents. (This does not apply to Brits or Americans playing ancient Egyptians, Greeks, Romans, et cetera, since we know everything is in translation anyway.)
Corollary to the above: bad translations of foreign dialogue, sometimes done for more “dramatic” effect (like “I am the sword of Almighty God” instead of “I’m your worst nightmare”).
I know that bird calls can completely ruin the illusion of being in another land and/or time for those familiar with them. So can inappropriate music, dialogue, costuming, props and so on (like seeing white sugar cubes served with tea in Pirates of the Caribbean).
Another car chase related one: When they dub in the sound of squealing tires, but the cars are on a dirt road. I can’t think of any specific examples, but I know I’ve seen it in a few 1960s-70s era movies.
I used to be this way with the unrealistic computer interfaces you always see in movies, but I have come to accept that the purpose of computer screens in movies is to show the audience what’s going on, not to be realistic.
Somebody working the action of a firearm to be threatening and no round is ejected. So the action movie hero has been running around, frequently in a firefight that’s been ongoing, with an empty chamber. I always find myself expecting the person threatened to laugh instead.
This one probably applies more to TV than movies, but older special effects that may have looked convincing enough on a small screen in standard definition, but look obviously fake when you see them on a bigger screen and in HD. For example I rewatched the Stephen King miniseries The Langoliers (1995) on Netflix a few years ago, and the CGI effects looked like something out of a 1990s video game.
When characters traveling in a vehicle have an intense conversation, and the driver spends minutes at a time looking at the person in the passenger seat, with nary a glance at the road ahead.
Yeah, I know you’re on a process trailer and not actually driving. Fake! LOOK AT THE DANG ROAD!!!
When scientists in movies set in current times refer to ideas or theories that have long since been shown to be wrong
E.G. in the movie Lucy when Morgan Freeman’s character brings up the old idea that humans only use ten percent of their brain
Phones…look, I can get past the idea that no one ever, ever says ‘bye’ when on the phone in a movie or on TV, they just hang up What bugs me is when someone hangs up and there’s a dial tone…on a cell phone.
I assume they’re doing it to make the other person hanging up sound more dramatic, but a simple beep (and the character looking at their phone) would make a lot more sense. Those foley artists can’t all be so old they don’t understand how cell phones work.
Corollary: The camera switches POV from the driver to the passenger and back, and their windows go from being open to closed and back again ad infinitum. This happened all the time whenever Jim had someone with him in his Pontiac on The Rockford Files.
Mundane unrealistic things in unrealistic sci-fi movies.
Battleship:
Alien invasion vs USS Missouri museum ship=okay.
Screw-up criminal becomes a US Naval officer: Um, no.
Abraham Lincoln Vampire Hunter:
Ninja Abe vs Vampires=okay.
Walking silver ammo to Gettysburg overnight: Um, no.
Another driving one: when the driver is talking to the passenger and turns their head to face them, and doesn’t look back at the road for far longer than feels normal. When it results in some type of accident, I understand, but no competent driver goes 10 or 15 seconds without at least glancing forward.
In the realm of retconning: it’s kind of funny to imagine reasons why the characters would be, with lightning rapidity, raising and lowering the windows repeatedly—with neither of them ever referring to the fact at all.
(Well, not terribly funny. More ‘bizarre,’ I’ll concede.)
Isn’t that what I said?