Edit
An old Danish folktale about a vain and hedonistic emperor who gets fooled into walking around town while "wearing" supposedly invisible clothes that only smart people can see, and his people being reluctant to believe and/or admit the truth until an innocent child points out that the emperor is actually completely nude. Known in Japan as "Naked Emperor".
The name is sometimes used idiomatically to describe the phenomenon of pluralistic ignorance.
Apply this tag when the character alludes their state of nudity to the folklore (such as referring their cloth as the one that only X could see, etc.), or depicts the scene of the original tale.