The use of the Moron Beam can be identified by the screams of "NOOO! Why did you DO that?!" from fans who recognize that the character in question really should have known better. Fanfic, particularly badfic, is riddled with this sort of thing, but examples appear in canonical works, too.
If you must use the Moron Beam, it ought to at least be lampshaded.
- Farscape: Surely the Peacekeepers built proximity sensors into their Prowler ships. Surely Aeryn should have noticed the pod coming down on top of her like that. Nope—they got her with the Moron Beam.
- LotR movies: "I've got a great idea! Let's take the Hobbits to Osgiliath!" ... Poor Faramir.
- Also when Frodo sent Sam away on the Steps of Cirith Ungol.
- Star Wars: "So this is how liberty dies—with thunderous applause." Apparently the entire Senate got hit with it.
- Jean-Luc Picard in the Marrissa Picard series, starting when he adopted her.
- Any time Elrond appoints a Mary Sue to the Fellowship, especially if he says "Ten Walkers" like it's supposed to mean something.
- That Series: Why would you put important parts of your body in someone's mouth and tell them that if they bit down you would, quote, "still" kill them?
As PPC Tech
The Moron Beam has been harnessed and developed into a tool for use by PPC agents. It looks and works like a flashlight. When the beam is shined on a character, whatever brain power they have is briefly suppressed. While this may make a character more suggestible or likely to accept things they otherwise wouldn't, such as the presence of a PPC agent about to kill them, it may also make them more prone to doing stupid things the agents don't want them to do, as was the case when Tawaki and Dustin tried it on an overpowered Gary Stu. Therefore, it should be used with caution.