Non-Lethal Deadly Weapon

A weapon has been established as ineffective or non-lethal, but the characters still act like it's real and dangerous. Often this is Fridge Logic, because the non-lethality of the weapon is established after someone is threatened with it.

Probably most common in cartoons, as a result of Never Say "Die". In videogames, this is a common type of Cutscene Incompetence.

Related to Selectively-Lethal Weapon and Cut His Heart Out with a Spoon. Contrast Nerf Arm.

Examples of Non-Lethal Deadly Weapon include:

Anime and Manga

In Bleach, during the Kasumioji Clan filler arc, a character named Kenryu is introduced. His Empathic Weapon is Benishidare, which sprays pollen in the air, and any weapon that it lands on is instantly covered in flowers. That's right, he fights by covering his enemies in flowers.

Film

In the live action Super Mario Bros. film, an old lady attempts to mug the titular pair using some kind of cattle prod. She touches Mario with it, but he acts more surprised than incapacitated or in pain. Since there were two of them, they could've easily overpowered her even if she tried shocking one of them for a longer interval.
In Prince of Space the title character repeatedly states that his enemies weapons cannot harm him. Despite this he always jumps out of the way when they shoot at him. Apparently this is a result of the dub, in the original script the bad guys were apparently just ridiculously poor shots.
Subverted in Weird Science, where the female lead uses a massive Hand Cannon to threaten a few characters before revealing it is a harmless, but incredibly realistic, prop water pistol. The male lead eventually uses it to threaten the Hell-Bent for Leather Badass Biker. He then fails gun safety forever by flagging everyone in the crowded house. Predictably, the weapon discharges a real round.

Live Action TV

Played for laughs in "Self Defence Against Fresh Fruit" sketch by Monty Python's Flying Circus.
Star Trek: The Original Series episode "Patterns of Force". A Nazi fires a gun at a Resistance fighter and kills him. After Kirk and Spock grab the Nazi, Spock takes her gun away from her. The fighter then gets up, revealing that her gun was filled with blanks. Spock points the gun at the Nazi, even though it can't shoot her. Watch it here, starting at 4:40. Perhaps justified by the fact that even blanks can cause serious injury from the range he is threatening her with it. (And from the look on her face when this happens, she agrees.)
Played for laughs in British comedy Vexed in which an Axe Crazy Woman Scorned decides to kill herself, her lover and the male lead by burning them alive. The two men beg hysterically for their lives as she soaks them in petrol and lights a match. Turns out it was diesel.

Western Animation

Looney Tunes - exactly how is Elmer Fudd planning on doing any hunting with a gun that just covers the target in soot, or some other comical effect?
In Dinosaucers, the bad guys hold a human hostage by threatening to freeze him with liquid oxygen. They end up getting hit themselves, this turns them into ice statues, but they get better pretty quickly. This makes one wonder why everyone was so worried about the hostage in the first place.
In The Flintstones animated movie The Man Called Flintstone, two thugs attempt to assassinate Fred with a some sort of rock pistol. It misses and ricochets hitting one of them, apparently nothing more than an irritation. Now the 'bullet' would have lost some momentum by that time, but still.