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.
According to Quora it takes 5 minutes, with a willing participant.
Anaesthesia that’s injected right before an operation can knock you out in about 30 seconds (and until then you could still struggle, technically speaking), but that’s a thick-ass tube of drugs they’re pumping inside of you. Some vapours from a rag is going to do jack shit.