plastic dull knife

1. referring to the actual, plastic dull knife
2. a useless trick/weapon against something more powerful/clever trick

Ex 1.
"Is that a plastic dull knife? why are you borrowing it here?"
Ex 2.
Generic Hero: "I WILL SMITE YOU WITH MY SWORD."
Villain: "YOU PULL A PLASTIC D U L L KNIFE TO MY TRICKERY!!!"