Fish Eyes

Mega Man's eye replacement didn't work out as well as he'd hoped.

"I can't stop looking into those entracing eyes... Can she see all around her? Maybe she can see through the very fabric of time and space!"

—Phoenix Wright on Derpy Hooves, Turnabout Storm

How do you make a blank stare even blanker? Have the character's eyes face slightly (or even more than slightly) away from each other—reverse cross-eyes, if you will. It's usually used to make the character look unintelligent or dumbfounded, causing it to become known as "derp eyes" in some Internet circles.

A particularly common form of Off-Model in both hand drawn and computer generated 2D animation, especially when depicting an aside glance.

This is not to be confused with Mismatched Eyes.

Examples of Fish Eyes include:

Anime and Manga

Depending on the angle, Ryuk from Death Note can have this in spades.
Caster of Fate/Zero has these, emphasising that he's not the world's most stable individual.
Katou from Holyland, emphasising how nuts he is.

Film

Ed the hyena in The Lion King.
Maruti from The Return of Hanuman does this sometimes, either to show he's crazy or that it's because of technical problems.

Literature

A minor character in the Discworld books is Nobby Nobbs' on-again off-again girlfriend, a fishmonger named Verity Pushpram. Three guesses as to why she's nicknamed "Hammerhead".

Live Action TV

Cookie Monster of Sesame Street has eyes like this. It's apparently why he's Marty Feldman's favorite Muppet.

Newspaper Comics

Matt Groening's Life in Hell would use a slight wall-eye effect on characters who were despairing about something. Doubtlessly influenced the early Simpsons examples.

Video Games

All passive (harmless) mobs in Minecraft. Since eyes are only two pixels wide by one pixel tall, it was either that or crossed eyes, which are used for the default player character skin and for wolves and ocelots, to make them look more intelligent.
Masada (or that guy with the piano) in Yume Nikki.

Web Original

Parodied in The Angry Video Game Nerd episode "Game Glitches" during the Rocky part, when the Glitch Gremlin changes Rocky Balboa's face by making his eyes pop out, and calls him "Bug-Eyed Balboa".

Western Animation

As shown at right, Ruby-Spears' Mega Man had this photoshopped to the point of Memetic Mutation.
In SpongeBob SquarePants, this is done a few times. Most notably in the episode 'Selling Out', done by the new manager, Carl. The only time he doesn't do this is when he narrows his eyes at Mr. Krabs, but he's back to his glasgow-style smile and literal fish eyes afterwards.
Luigi briefly wears this expression at the end of the Super Mario World episode "The Yoshi Shuffle".
Seen a few times in My Little Pony Friendship Is Magic, often as a Freeze-Frame Bonus:
- Derpy Hooves is an interesting case. Her Fan Nickname (which was adopted to be her canon name) comes from this, yet she usually inverts the actual trope: Her eyes are seen facing inward more often than outward (but they do face outward on a few occasions, so she still counts).
- One background pony in "Griffon the Brush-Off" can be seen making a crazy "shocked" face, complete with fish-eyes, when Fluttershy is scared off by Gilda.
- Rainbow Dash briefly wears this expression in "Fall-Weather Friends" while trying to laugh off Twilight's suspicions.
- Pinkie Pie wears this expression in "Party of One" whenever she is puppeteering the friends that she created for Gummy's after-birthday party.
- Twilight Sparkle lapses into this several times during her brief struggle with mental instability in "Lesson Zero".
- In the toys, Princesses Celestia and Luna tend to suffer from this. The Target-exclusive plush of Twilight Sparkle does too.
Pops up now and again on The Simpsons, especially on earlier seasons. There's even one episode where Marge is trying to talk some sense into him, and his reaction is to stand there staring off into space, with one of his eyes wobbling back and forth. Then the same scene is repeated with Bart and Lisa in the same episode.
Ren from Ren and Stimpy has them from time to time.
- MANY characters from Ren and Stimpy have fish eyes when drawn in an "off-model" way. Ren's pretty obvious, though, because he's a chihuahua.
Done in The Adventures of Jimmy Neutron, in the movie Attack of the Twonkies. The Twonkies often wear this expression.
In Ed, Edd 'n' Eddy, this is Ed's default expression.
The hotelkeeper in episode 2 of Scooby-Doo! Mystery Incorporated has constant Fish Eyes.
Cartoon depictions of Rodney Dangerfield sometime veer into this when he's playing stupid: see Rover Dangerfield and the Genie's impression of him in Aladdin.
Megatron and Starscream Narmfully don this expression several times in Transformers Prime.

Real Life

Can occur in Real Life as a result of a disorder known as exotropia.
Can also occur in real life as a result of a disorder of the eyes called "Strabismus," which causes the eyes to face in odd directions. It can be treated through eyepatch therapy, or cured through surgery.
The late great Marty Feldman. And despite having Graves' disease, he was a talented actor and a great comedian.
George Harrison of The Beatles. That didn't seem to matter to any of his thousands of fangirls, though.
Indie comic artist/storyboard artist of Adventure Time fame, Thomas Herpich. He's still a pretty handsome guy despite his odd-looking eyes.
The man of the "Are You A Wizard?" meme.