Martijn van Teffelen

General introduction 11 1 HOSTILITY: AN EXPLOSIVE MATTER Many, if not all human beings experience hostile thoughts, angry feelings and yell or curse at some point in their lives. Several may even physically hurt another person. In psychology, human antagonistic behavior and its’ related cognitive-affective experiences are often referred to as hostility. Possessing some degree of hostility can be considered healthy. From an evolutionary standpoint it can be argued that the chances of surviving a physical threat (e.g., being attack by a wild animal) increase when the intentions of someone or something in the outside world are correctly identified as threatening. Motivating oneself to behave aggressively in response (e.g., by shouting or launching a physical attack) may scare off or neutralize a threat. Correctly identifying the potential wrongdoing of others and reacting with an angry response may prevent harm. However, hostility becomes more problematic, when a person becomes angry with the wrong person, to the wrong degree, at the wrong time, for the wrong purpose, and in the wrong way. A tragic example of problematic hostility is the case of Shahid B., in the media portrayed as the ‘wedding procession whacker’ (“Cel en behandeling voor Rotterdamse ‘trouwstoetmepper’,” 2020). At the age of 26 Shahid B. took part in a wedding procession of his brother. When a police officer stopped the wedding procession due to nuisance, Shahid B. got out of his car and physically assaulted the police officer, who entered unconsciousness for a short period. Shahid B. declared that it was not his intention to act violently. He said: “But that is who I am. I cannot help it. I become too angry. I wanted to stop the situation because my brother-in-law did not do anything wrong. I am sorry about this.” DEFINITION OF HOSTILITY In psychological research, hostility is defined as a personality dimension consisting of a tendency to hold a hostile attitudinal style, experience angry affect and behave aggressively (American Psychiatric Association, 2013; Barefoot, 1992; Chaplin, 1982). Profound consequences of hostility are increased risk of interpersonal violence (Henrichs et al., 2014), heart disease (Smith, 1992), increased psychopathological severity (Cassiello-Robbins & Barlow, 2016), treatment discontinuation (Arntz et al., 2015) and suicidality (Ammerman et al., 2015). Clear prevalence estimates in patients are currently missing. However, one cohort study in N = 3800 psychopathology outpatients indicated that 43.60% ( n = 1657) reported moderate to severe anger and 21.20% ( n = 806) reported moderate to severe aggressive behavior in the preceding week (Genovese et al., 2017). Problematic hostility is often a primary reason for people to seek help (Lachmund et al., 2005). Traditional classification instruments, however, do not describe a ‘hostility disorder’. The DSM-V (American Psychiatric Association, 2013) for example, captures (aspects of) hostility as