Then there's the infamous metaphor of the sun being "pasted like a wafer in the sky", quite possibly the most famous line in the book. The amount of people who believe this must refer to a communion wafer is enormous.
Faux Symbolism: The cheerful dude that helped Henry find his regiment after Henry run away? Numerous interpretation agreed that he's just a cheerful dude.
First Installment Wins: Did you actually know there's a sequel short story titled The Veteran? Don't worry, you're not alone - That Other Wiki's page on The Red Badge of Courage shows how much people think of it by practically only mentioning that said sequel exists and confirms the preceding novel takes place in Chancellorsville.