A disguise that is so "thin" that the audience can immediately recognize who the person behind the "mask" actually is. Note that this doesn't require an actual mask; the character may have merely styled their hair differently, added glasses, or changed into a different outfit. Regardless of exactly what was used for the disguise, the identity of the character is completely clear, usually before they remove it.
Several external factors influence this trope. If the big-name Special Guest is going to spend most of the episode or film wearing a disguise, then you'd want it to be "thin" enough for audiences to identify the actor before The Reveal. If the character frequently wears disguises, then it may be a stylistic choice to reassure the audience as to the identity of the character. This is more common in media aimed at younger audiences, but is also common enough for Master of Disguise characters so that the audience isn't constantly guessing as to which character is "really" in disguise. The trope is still an important dramatic convention in live theatre and opera productions — where a really good disguise would render the character unidentifiable from the cheap seats, and be beyond the scope of the prop budget to boot — but is usually employed along with some kind of nod to audience acknowledging the absurdity.
Internal story factors also apply. If the disguised character is supposed to be foolish, wearing a bad disguise provides plenty of opportunity for comedy. A character who can't identify someone just because they added sunglasses to their ensemble is another way to mock disguises as well as genre conventions.
Classic examples of "bad disguises" are the following (tropes are linked based on their overlap, not subtrope status):
- Wearing a face-obscuring cloak or hat over the character's standard outfit.
- Wearing a Groucho Marx glasses-and-mustache prop.
- Putting on or taking off glasses/sunglasses.
- Changing out of a Limited Wardrobe, especially into a uniformed service, such as police officers or package delivery employees.
If the disguise is improved (such as by combining two or more "thin" details and changing your voice), you get an example of Wig, Dress, Accent, where the inability of the other characters to identify the disguised character becomes much more reasonable. In order to qualify as a Paper-Thin Disguise, there must be at least one obviously clear element of the character underneath. However, the probability that other characters are fooled by this disguise is just as fluid as with other disguise tropes.
It's becoming a bit common nowadays to subvert this trope by fooling the viewers instead, showing what seems to be a terrible disguise, but then it's revealed that it isn't, you thought that Bob was badly disguised as an old man, but then Bob in regular clothes appears next to that old man that looks like him.
Compare with Clark Kenting (a subtrope where the disguise is used over a long period of time and remains effective despite that) and Newspaper-Thin Disguise (where a book, magazine, or similar is used to hide a character's face).
Contrast with the vast majority of other Disguise Tropes.
