Many years ago in a D&D game, during a fight a player announced his character wanted to use his catapult. We all came to a stop. "Your what?" "My catapult." "...Where are you keeping a catapult?" "In my pocket?"
The GM had just let people buy whatever was listed in the blue box equipment list when we stopped off in a town, and the fact that the catapult cost 500gp had not rung any alarm bells for the player.
TL;DR: He thought he was walking around with this:
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and was actually walking around with this:
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Hilarity ensued.