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.
Hearing the exact wrong part of the conversation, and then making a horrific assumption and spinning off into zany misunderstandings instead of, just, “Hey, what did I just hear?”