Many animated shows, especially Japanese ones, have a habit of giving a character (sometimes more than one) an over-sized forehead. For some reason, the character, even if their head is their Berserk Button, will always take good care of their forehead, for it will always be as clean and shiny as possible. If not shinier, to the point where a common gag is to have others be literally blinded by the glare reflecting off their dome. This type of forehead could also be emphasized with the right hairstyle. Compare the less realistic My Brain Is Big.
Krillin, who had "Blind the enemy with the gleam off my cue ball" as one of his special attacks early on.
The Androids also have noteworthy foreheads. No wonder 18 married Krillin.
Also, one of the side effects of Super Saiyan II and III stages is a bulging forehead. Especially noticeable in stage III, where the lack of eyebrows makes it look even bigger.
Vegeta's is so notable it became a meme in Japan.
this could be said to be a trait of Akira Toriyama's art-style in general.
Yue Ayase in Mahou Sensei Negima!. One of the OAVs had a scene which started as if it were looking at a character through a Fish Eye Lens, only to pull back and show it was the reflection off Yue's forehead.
In the manga at least, characters remark on this, referring to her as "big forehead chibi" a few times. Chamo once even refers to her as the chick with the "Forehead of Doom".
An early Black and White silent movie of Dr. Jekyll and Mr. Hyde had Hyde develop a monstrously large forehead with the hair sitting on top rather like a cap and then dangling down to emphasis the scalp. The character would wear a top hat and then slowly pull it off to reveal the ongoing forehead.
Anthony Hopkins makes best use of his as Hannibal Lecter in The Silence of the Lambs, particularly in his last meeting with Clarice wherein as he probes her for details of her worst memory the camera focuses closer and closer on his lowered head, pale blue eyes glowering from under a hugely emphasised forehead.
Jeff: Oh come on, my forehead is not this big. [Everyone else in the room avoids eye contact with him.]
Seinfeld: Elaine Benes was called "big-head" by a bad date. She brushed it off until a pigeon crashed into her head.
Gina Waters' big head was a running gag on Martin. Thanks to the magic of TV genetics, she passed the trait on to her son on My Wife and Kids.
In the final episode of Red Dwarf's sixth series 'Out of Time', Lister (who have been locked in his quarters along with rimmer and the Cat on receiving contact from their future selves to protect them from the psychological harm knowing their future may cause) observes the future-crew's arrival by camera to see what happens to him (Kryten, having failed to cover up the fact something horrific had happened although refusing to specify). The glare off future-Cat's bald head obscures his view.
The Emergency Medical Hologram from Star Trek: Voyager has a shiny bald head, lampshaded in one episode when the Doctor becomes a celebrity on an alien planet and insists that the ship's engineer B'Elanna Torres design an opera house for him.
B'Elanna: "What's wrong with the sight lines?"
EMH: "If you consider the height of the average Qomar, it's obvious that anyone seated in the back five rows will have an obstructed view!"
Apollo Justice in his eponymous game. Klavier Gavin, the opposing attorney, refers to him as "Herr Forehead" (Mr. Forehead). Mind you, the name started with a forehead-related piece of evidence, but it fits nonetheless.
Maggey Byrde also has a large forehead and is known as the "Goddess of Misfortune".
Blue Mary had one in Fatal Fury, due in large part to being "inspired" visually by Android 18. Her head's proportions have shifted to more reasonable levels since.
Iori Minase in The Idolmaster, to the point that Miki Hoshii often calls her "Deko-chan" (from odeko, which means "forehead").
Her Puchidol equivalent, Io, is even able to fire destruction beams from her forehead.
JFK: I can't see! Due to the glare... of Mena Suvari's enormous FOREHEAD!
Jimmy Neutron's peanut shaped head has a bountiful forehead (to hold in all that mad science, you see) with it's shape exacerbated by his large upthrusting hair cut.
Betty Boop whose design was the basis of the beginnings of the modern anime style.
Stewie Griffin from Family Guy has a large forehead to emphasize both that he is a baby and that he is sort of a mad genius plotting to take over the world. Plenty of doom involved.
Beavis and Butt-Head had a yin-yang take on this. One (Butt-head) had a face where the eye and nose were raised up so he had a very large head with the face splayed out over it while the other (Beavis) had his face scrunched up low down with a pronounced overbite for emphasis so that he had a lot of forehead space.
Noah from Total Drama, although it's more unrealistic head proportions than anything else (his hair covers most of it).
The Brain. It occasionally causes him problems, like trying to slip through a chain-link fence Pinky goes through easily.
Dib. G.I.R. hides easily behind his noggin while infiltrating an enemy base.
In Superjail!, try not noticing the size of Jared's forehead.