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.
Lazy villain characterization. Someone dresses in black or snarls a lot or is albino or has some physical marker that makes them different from others, therefore they are the villain.
It is almost impossible for a character in a Hollywood film to speak with a Slavic accent and smoke a cigarette without also being some sort of asshole.