oh and in any murder mystery ever if one person killing is seen someone else thell kill 1-50 more not to get caught … what makes it dumber is sometimes no one catches the original murder but they get tripped up on murders 2-5… (Colombo and murder she wrote having the same creators and writers were good for this )
If a person decides to stay behind to hold off the monster, the other characters will argue with them for a time that is significantly greater than the amount of time “bought” by the individual’s sacrifice.
If people here want to save some time, we can take it as given that every single thing that’s been bothering us about TV and movies has an entry on tvtropes.
Because these go-to situations we’re noticing are ALL tropes! And I love that – it’s a tribute to the commonality of humankind that the lazy writing that’s been bugging me for years has been bothering everyone else, too.
Like, in the recent deluge of medical shows, the way-too-young, way-too-attractive doctors don’t play by the rules. And their mavericky rebelliousness saves the patient, yay! Except… you probably want a doctor who’s got some experience and plays by the rules, because those rules tend to have a proven track record of, y’know, saving patients.
“Something Vimes had learned as a young guard drifted up from memory. If you have to look along the shaft of an arrow from the wrong end, if a man has you entirely at his mercy, then hope like hell that man is an evil man. Because the evil like power, power over people, and they want to see you in fear. They want you to know you’re going to die. So they’ll talk. They’ll gloat.
They’ll watch you squirm. They’ll put off the moment of murder like another man will put off a good cigar.
So hope like hell your captor is an evil man. A good man will kill you with hardly a word.”
― Terry Pratchett, Men at Arms
That one always drives me crazy. Even worse is when they run a few feet away, then stop and watch the first guy get killed before continuing to run.
Any person who has been continuously emperiled/kidnapped/tortured will get one chance to escape by lightly bonking the bad guy over the he head with a conveniently placed blunt object when he lets his guard down/turns his back. The victim will then immediately drop their weapon and run, instead of pounding the bad guys brains into pudding.
That one always gets me. I can think of at least four films where Cary Grant wearily bleats that one out.
Or maybe I’m thinking of Yul Brynner.
Or when former child actors go without eyebrows in films, we know that they’ll always end up creepily prognosticating the fate of the homicidal, metamorphosing, sax-blowing protagonists.
Firefly had a lampshading of that in the pilot episode. When Book goes to check on and warn the fed, the fed knocks him out with a blunt object (futuristic fire extinguisher?). Book slumps to the floor, and the fed gives him a few more thumps for good measure.
Averted on Babylon 5, when Sinclair was rescued from the torture chamber he’d been imprisoned in. He did NOT show any mercy to the inquisitor who’d been working to break him.
When [someone who has lived in a magic place of perpetual youth for centuries decides to leave] in a movie/on TV, we know that [rapid aging] will happen
When the red lights in the killer robot’s eyes go out, you know that the robot has been rendered inoperable. It’s not necessary to know anything about the robot’s operating system. Lights go out, it’s dead.
At least until the auxiliary power source kicks in. 
Actually Lt. Shea disputes this one:
Oh, and if Dean Norris is in it, he’s playing a cop.
This may be endemic to British mystery series, but if you go for a walk alone, someone will be murdered and you’ll be the prime suspect since you have no alibi.
If a dangerous piece of machinery is shown, someone will be killed by it.
Also in British mysteries, when the detective explains who the murderer in the end, the killer will admit to it instead of refusing to say anything without his lawyer present.
The first person arrested in a British murder mystery is never the criminal. Father Brown takes this trope to ridiculous lengths by arresting people on the flimsiest of pretexts.
I assume you’re referring to a TV series? I don’t remember many arrests in the stories by Chesterton.
Also, killer robots will always have red eyes or other indicator lights. Good robots will be green or blue.
So when a good robot is corrupted, the light will turn red.
Knowing this, when I get ready to take over the world my murderbot army will only have green lights with no option for any other color. The heads will also be purely cosmetic with only redundant and disposable sensors in them.
In the (usually delightful) short stories*, Father Brown is so harmless-looking and secret-eliciting that the criminal ends up realizing his only logical step is confessing. Not many arrests happen “on-camera”.
Though they may have had to “punch 'em up” for television… more’s the pity.
In The Blue Cross* (an utterly delightful short story this time), he unmasks a fake priest through mayhem-causing illogical acts.
And the last line… oh, go read it, it’ll take you ten minutes, tops.
How about from the world of cooking shows? On a cook-off or some such show when they do the backstory of a chef in their restaurant there will always be a pan on fire at one point.
There’s a zillion things a chef has to be able to do but a pan on fire is apparently the only thing that counts.