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.
Whenever the plot entirely revolves on avoidable misunderstandings from character that nothing in the story prevents from having a clarifying chat. It’s weak storytelling.
Also whenever the characters don’t react to enormous thing A because advancing the story requires them to immediately ask about thing B.
Lastly whenever you end up screaming at the tv “you have enough clues to call for backup” or “enough reason to worry to call 911” yet they proceed alone. Bad writing.
“We don’t have time (to explain why were doing this)”
Proceeds to have time to do dozens of other useless things
You didn’t watch a lot of Three’s Company, did you? :-D