Maybe they’re always hungry, maybe there’s some deep metaphor linked to apples, but villains are constantly shown eating apples in movies. There are many tropes in cinema, some more frequent in certain genres than others, such as the “final girl” in horror movies or the “unrequited love” in countless romantic comedies.
There are many types of villains in movies, and they all have different quirks and styles, but they usually share one or two characteristics. Some really like having a pet by their side, and others love having evil sidekicks, but there are others that are really into eating while playing their villainous role – and they don’t eat just anything. Turns out that villains are into apples, and it’s not a recent trend.
Villains eating apples is a trope that has appeared in different movies from various genres, and it’s a way to represent arrogance and confidence – because if there’s something these characters don’t have to worry about is lack of confidence (e.g. Ajax in Deadpool). Eating an apple while talking or while another character talks is also a way to show dominance and that what the other character is saying is irrelevant to them (for example, Draco Malfoy in Harry Potter and the Prisoner of Azkaban, eating an apple during Hagrid's class). Colin Farrell's seductive vampire in Fright Night had a fondness for apples (perhaps the vampire equivalent of a nicotine patch in between biting necks), and Hector Barbossa couldn't get enough of apples in the Pirates of the Caribbean movies.
Why apples? Because they have a distinctive sound when someone bites them, and this “crunch” blocks the sound (again, what the other character is saying means nothing to the villain), and draws attention to them. Some of these apple-eating villains also tend to toss it away after one or two bites, adding to the arrogance of the character – and apples, being a common fruit with a sound effect that works on the character’s favor, are the perfect food to toss away on camera.
The most obvious origin for this trope is the Bible's original sin of Eve biting into an apple offered by the Devil. As such, the apple represents temptation and a loss of innocence, and villains who either consume apples or offer them to the protagonist are symbolically aligned with evil. Drawing from the same story, applies are associated with knowledge, and a villain smugly biting into an apple is a shorthand for suggesting the upper hand. Farrell's Fright Night character is a prime example of this; he smiles and bites into an apple after allowing the hero to "escape" with a damsel in distress, knowing that she's already turned into a vampire and will burst into flames as soon as she steps into the sunlight.
Another classic link between villains and apples is the fairy tale Snow White and the Seven Dwarfs, in which the Evil Queen gives a poisoned apple to Snow White - which in turn may have been inspired by the Bible story. As with so many tropes, the more it's used the more effective it becomes at communicating a certain meaning to the audience. However it may have started, the apple is an easy way to tell the viewer that a certain character is up to no good.