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.
Tropes are not something one should avoid at all times. Tropes are there because they work. It’s the lazy use of tropes as a crutch that is the problem.