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.
Nonsensical or thoroughly debunked technobabble. The most annoying for me is faster than light communication via quantum entangled particles. Yes entangled particles will change each other’s state faster than light but this effect CANNOT be used to send information of any kind. At all. Ever. This has been known since engagement was first discovered but Hollywood is always like “I’m just going to ignore that second part.” I don’t even have anything against ftl comms or any other physics breaking things, just use an explanation that isn’t literally impossible and well known why it’s impossible for God’s sake.