Katagelasticism is a psychological condition in which a person excessively enjoys laughing at others (coined by Christian F. Hempelmann and Sean Harrigan from ("katagelastēs"), Ancient Greek for “mocker”). Katagelasticists actively seek and establish situations in which they can laugh at others (at the expense of these people). There is a broad variety of things that katagelasticists would do—starting from harmless pranks or word plays to truly embarrassing and even harmful, mean-spirited jokes. They would be of the opinion that laughing at others is part of the daily life and if others do not like being laughed at, they should just fight back. For the katagelasticists it is fun laughing at others and there is almost nothing that might hinder them from doing so. For them, some people even might provoke getting laughed at (and surely deserve being laughed at). This condition often makes it difficult for sufferers to gain and maintain acquaintances and romantic partners.

The first academic paper to investigate this phenomenon was published in 2009. Along with gelotophobia and gelotophilia it can be measured through a questionnaire that consists of 45 questions (the PhoPhiKat-45; the PhoPhiKat-30 is a short form that consists of 30 items). This is a reliable and valid instrument that has been used in a variety of studies. The questionnaire is also online for a free self-assessment in an English form at gelotophobia.org and in a German form here.

Gelotophobia, gelotophilia, and katagelasticism describe three different stances towards laughter and laughing at. Empirical studies with the PhoPhiKat-45 show that, of course, people can not at the same time fear and like being laughed at (i.e., be gelotophobes and gelotophiles at the same time). However, there is at least a subgroup of gelotophobes that enjoys laughing at others, despite knowing how harmful this can be. Finally, gelotophilia and katagelasticism are positively related; i.e., those who enjoy being laughed at might also enjoy laughing at others.

Gelotophobia is a fear of being laughed at, a type of social phobia. While most people do not like being laughed at, there is a sub-group of people that exceedingly fear being laughed at. Without obvious reasons, they relate laughter they hear to be directed at themselves. Since 2008, this phenomenon has attracted attention from scholars in psychology, sociology, and psychiatry, and has been studied intensively.

In his clinical observations, found that some of his patients seemed to be primarily worried about being laughed at. They tended to scan their environment for signs of laughter and ridicule. Furthermore, they reported that they had the impression of being ridiculous themselves. Additionally, Titze observed a specific movement pattern among them when they thought they were being laughed at—awkward, wooden movements that resembled those of wooden puppets. He described this state as “Pinocchio-syndrome”.

Two other behaviours related to laughter are gelotophilia - "the joy of being laughed at" and katagelasticism - "the joy of laughing at others".

From the clinical observations a model of the causes and consequences of gelotophobia was drawn up so that the condition could be studied scientifically. The model claims that gelotophobia can be caused by any one of three things at different stages of development:

The putative causes of gelotophobia:

- In infancy: development of primary shame failure to develop an interpersonal bridge (e.g. unsupportive infant–caregiver interactions).

- In childhood & youth: repeated traumatic experiences of not being taken seriously or being laughed at/ridiculed (e.g. bullying).

- In adulthood: intense traumatic experience of being laughed at or ridiculed (e.g. ).

The consequences of gelotophobia:

- Social withdrawal to avoid being ridiculed.

- Appearing ‘cold as ice’/humourless.

- Psychosomatic disturbances, e.g. blushing, tension headache, trembling, dizziness, sleep disturbances.

- Demonstrating ‘Pinocchio Syndrome:’ clumsy, ‘agelotic’ face, ‘wooden puppet' appearance.

- Lack of liveliness, spontaneity, joy.

- Inability to experience humour/laughter as relaxing and joyful social experiences.

- Anger when being laughed at by other people (in some cases this results in violent attacks on the people who were laughing).

Later this model was revised and expanded.