I’ll go first. Mine is the instant knockout drug. Like Dexter’s intramuscular injection that causes someone to immediately lose consciousness. Or in the movie Split where there’s the aerosol spray in your face that makes you instantly unconscious. Or pretty much any time someone uses chloroform.
Cutting or stabbing through full plate armor with a sword. Why would anyone wear an armor that is easily cut or stabbed through?!
A lot of that sort of armor is more designed to deflect hits off of it. If someone can get a solid hit in, it’s possible to cut through it.
Which leads to another pet peeve of mine, which is armor that’s clearly designed in a way that it wouldn’t be good at deflecting hits. Particularly anything for women that has cups for the breasts.
In real life it’s more like going after a man sized can of tuna, with the bastard child of an axe, a hammer, and a crowbar.