One common joke to show that a character is not very bright is to give them issues with reading and writing. Obviously there is is some similarity with the use of dyslexia in fiction but there is a subtle difference; with this trope the use of illiteracy is a joke to establish or confirm a character's stupidity rather than a joke about dyslexia as such.
- If a character is of normal (or better) intelligence then the trope is probably "L" Is for "Dyslexia", even if it is used for a joke. Likewise if the character is irrelevant or not even present for the joke (ie. the newspaper headline "Dyslexia For Cure Found")
- If a character is otherwise The Ditz then it is probably this trope.
Examples: Comic Books
- The page image comes from the 1950s comic Dizzy Dames which enjoyed using this joke. Another version had Moronica walking cheerfully across a lawn and telling off a cop who tried to stop her by pointing at a 'Please Stay Off The Grass' sign ("See - Police Stay Off the Grass.")
- In the film version of Harry Potter and the Chamber of Secrets, when Harry disguises himself as Goyle, using Polyjuice Potion, he forgets to take off his glasses. When Malfoy notices it, Harry quickly says he was reading. Malfoy asks (either cynically or with genuine surprise): "You can read?"
- In one Three Stooges short, the stooges play managers to a prizefighter. When the fighter hits his head before the big match and is knocked unconscious, Moe tells Shemp to go get some ammonia (i.e. smelling salts) to wake him up with. Since Shemp can't read very well, he gets a bottle of ether instead, because it says, "for insomnia" and he confuses the words insomnia and ammonia. Needless to say, this doesn't help the boxer's condition any.
- In an Abbott And Costello film whose name escapes me, they're at a restaurant and the waiter points out a sign saying (I think) "Watch your hat and coat." Costello replies, "Who's smoking?"
- Kelly Bundy from Married... with Children was often portrayed as barely literate. Or sometimes not even that
Kelly: Oh, the pressure. Kelly, you have to go to school. Kelly, you have to pass. Kelly, you have to learn to read. How am I supposed to grow up with all this hanging over my head?
- Used as one off gag on Drake & Josh. Resident ditsy guy Drake reads off that a rare pepper is from South Am-ER-RE-ka and wonders where that is. The pepper was actually from South America [[note Drake lives in the United States of America so he should have been familiar with the spelling/pronunciation]]. Another episode has him put in intensive English class, but that wasn't so much because of this trope, but rather having an English teacher that openly hates him.
- As of season two, Charlie in It's Always Sunny in Philadelphia is illiterate (or possibly dyslexic, per Rule of Funny). 
- Xena: Warrior Princess: When Ares is about to marry Xena, her Identical Stranger Meg is hired to jump out of the cake at Ares' Stag Party. She comes out wearing nothing but icing and chants "Gimmie an A! Gimmie an R! Gimmie an S! Gimmie an E! Whaddya got? Go Ares!"
- Dungeons & Dragons 3.X has it in the rules. Barbarians, stereotyped as Dumb Muscle, have to spend a skill point or take a level in another class to become literate.
- Despite what Touhou fanon often depicts, canon Cirno actually averts this. She's capable of reading and writing basic Japanese. By fairy standards she's a genius.
- Minmax in Goblins traded away his ability to read in exchange for being a better fighter. At one point, Forgath pranks him by convincing him his belt buckle, which has the words "I Am Great" carved on it, actually says "I am sexually attracted to small mammals".
- Homer Simpson has at least once claimed to be unable to read. From the same show Miss Springfield, Mayor Quimby's Dumb Blonde mistress, once mistook his sash saying 'Mayor' for 'Major' and thought he was in the army.
- The Merrie Melodies cartoon "Cat-Tails For Two" features the smaller cat George trying to capture Speedy Gonzales aboard a cargo ship. One effort involves fireworks, which ends with George getting blasted to a frazzle. The larger cat Benny seeks to comfort George with some water. He finds a bucket of liquid, and reads: "P-E-T-R-O-L. Huh, that's a funny way to spell water." Benny douses the smoldering George with the "water." It doesn't help.
- Thimbo, Corvax's not-too-bright sidekick in Muzzy in Gondoland cannot read.
- In the Looney Tunes short, "A Bear For Punishment", Junior Bear decides to fetch Pa his pipe on Father's Day. When he is looking for tobacco to stuff in the pipe, he finds a can, and reads: "G-U-N-P-O-W-D-E-R", thinking it's tobacco. As a result, the pipe explodes in Pa's face when Junior lights it.
- In another Bear short, Junior needs to put out a fire and grabs a bucket already full of liquid. "G-A-S. Sure is a funny way to spell water."
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