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.
But also "if someone slices you across the stomach with a big sword you don't bleed you just hold your stomach and fall over while going 'arrghh'"