Humor is a perceptual experience that causes people to laugh. By definition, it is generated by a 'sudden radical deviation from expected patterns of behavior in a situation that concludes by being non-threatening to the perceiver.' That behavior can be linguistic behavior (grammar, word usage, pragmatics), character and social behavior (deviations from etiquette and social norms) or normal situational and visual associations (incongruities).
Be aware in creating the characters in your story or screenplay that the source of much character humor is deviations from expected patterns of role behavior or social behavior. For example, the miser, the liar, the drunkard, the lazy person, the lecher, the gossip, the coward and the hypocrite are all comedic characters.
Pretense is a common trait of many humorous characters. An audience will laugh at any character that lacks self-knowledge - one who is a fraud and tries to publicly present him/herself as an authority figure deserving of respect. When exposed by other characters as a fraud, the audience will laugh. But when these pretentious characters then try to cover up and continue their pretensions, the audience will laugh again because these characters are no longer a threat to them.
Humans that take on animal characteristics, and animals that act like humans, such as the Cowardly Lion and many of the Walt Disney and Warner Bros. cartoon characters, are also examples of deviations from expectations. Their behavior deviates from what is expected of different kinds of creatures, whether human or animal.
Characters involved in embarrassing situations, pratfalls and small misfortunes are humorous and will generate laughter. Chevy Chase has made a career from this type of comic behavior. Some successful comedians develop a 'persona,' a character with an essential incongruity at the core of their personality. For example Steve Martin is the sophisticate who is socially inept, and Bill Cosby is an adult with child-like enthusiasms.
Other types of unexpected behavior that will generate laughter are silly walks, silly faces, silly sounds, silly body movements and funny gestures. A character can also suddenly deviate in the way that he speaks by playing with the rhythm, pitch, tempo, volume and timing of his movements or actions. He can also speak gibberish while presenting it as a meaningful utterance. Incongruity can also be expressed in makeup, hairstyle and wardrobe.
An exaggerated, understated or irrelevant response to the situation are all deviations from the normal expectations of behavior and will produce tension in the viewers who know what the expected behavior should be. This tension will be relieved through laughter if no real harm is done to the characters for which the audience has empathy -- with which they are emotionally involved. The audience will also laugh if harm is done to a character that the audience hates, such as the burglars in the movie 'Home Alone.'
Continual repetition of any behavior is also a deviation from the norm and will produce laughter. Another common comic type is the bumbler, best exemplified by Peter Sellers as Inspector Clousseau in the 'Pink Panther' movies. This character poses as an authority figure -- a police detective - that, in actuality, is an incompetent fool.
A character that does not learn from his errors and continues to make the same stupid mistake again and again will produce laughter. An example of this is the Rick Moranis character, Louis, in the movie, 'Ghostbusters.' He locks himself out of his apartment on three different occasions in this movie.
One process for designing comic characters that radically deviate from expected norms of behavior is to work with the framework of Aristotelian ethical theory. Aristotle, in 'Nichomachean Ethics,' designed a theory of virtues and vices. For each 'sphere of action,' he indicates a 'mean,' which is the norm or appropriate behavior for that type of situation. From this 'mean,' he then constructs an 'excess,' which represents the exaggerated behavior pattern for a type of situation, and a 'deficiency,' which represents the understated behavior pattern for this kind of situation. Extreme cases of either type of deviation from the 'mean' will produce laughter.
Following are examples of comic characters from some popular films classified in terms of the Aristotelian Ethical Concepts:
~~ Excess Character Traits
Vanity: Joker (Batman) -- Admiring himself in the mirror as his girlfriend Alicia watches.
Licentiousness: Peter Venkman (Ghostbusters) lusts after the female student during the ESP experiment.
Prodigality: Joker (Batman) throws money into the crowd at the Gotham City parade.
Ambition: Joker (Batman) wants his face on the one-dollar bill
Shyness: Forrest (Forrest Gump) -- Forrest is shy when Jenny first makes a sexual advance towards him in her college bedroom.
Boastfulness: Joker (Batman) -- Boss Grissom could not run Gotham City without him.
Buffoonery: Ray Stantz (Ghostbusters) -- Over-enthusiastic whenever he talks about the supernatural
Obsequiousness: Hotel Manager (Ghostbusters) -- He tries to placate clients waiting to use the Ballroom
~~ Deficient Character Traits
Cowardice: Sallah (Raiders of the Lost Ark) -- When Sallah sees snakes in Well of Souls, he tells Indiana Jones to go first.
Insensibility: Louis (Ghostbusters) -- At the end of the story, Louis is oblivious to the danger he has just experienced.
Cheapness: Uncle Frank (Home Alone) -- He will not pay for the pizzas.
Pettiness: Kevin's Sisters (Home Alone) -- They will not help Kevin pack his suitcases.
Timidity: Cowardly Lion (The Wizard of Oz) -- He is afraid to go in the Witch's Castle to save Dorothy
Lack of Ambition: Kevin (Home Alone): There is nothing he really wants at first but to be left alone.
Lack of Spirit: Egon (Ghostbusters) -- Egon is a scientific nerd, who is passive and indifferent to the sexual advances of the secretary.
Understatement: Venkman (Ghostbusters) -- Almost all of his reactions are understated
Boorishness: Egon (Ghostbusters) -- Egon is a scientific nerd whose only talks about his research topics.
Cantankerousness: Mr. Peck, the EPA Inspector (Ghostbusters) -- Self-righteous and very difficult to work with.
Shamelessness: Burglars (Home Alone) -- Marv brags that they are 'the wet bandits.'
Malicious Enjoyment: Marv (Home Alone) -- Stuffs the sinks so water will overflow onto the floor.
We all know what the appropriate rules of behavior are in social situations, and we know when they have been broken. To make an audience laugh, we have to write scenes showing our characters breaking these rules, being sure to allow that no real harm is done to any other character on the screen for which the audience has empathy. Write your characters and scenes using this technique, and the audience will laugh.