Psychological Inflexibility (PI) refers to the rigid dominance of internal reactions (e.g., thoughts, feelings, memories) over personal values and contingencies in guiding action. Previous research suggests that PI impacts negatively on emotion regulation. This study examined the effect of PI and gender on anger and aggressive behaviour in emerging adulthood, a developmental phase characterized by increased emotionality. Participants were 382 emerging adults (64.4% females; mean age: 22, SD = 2.9) recruited at the University of Pisa, Italy. Males and females were divided into two groups - high and low-PI - based on the Acceptance and Action Questionnaire-II scores. The STAXI-II was used to assess anger dimensions: expressing anger outwardly (AE-O), inward expression of anger (AE-I), attempts to control the expression of anger (AC-O), and inward control of anger (AC-I). ANCOVA analyses were conducted to explore the effects of PI and gender on anger. The interaction effect (gender x PI) was not statistically significant. Females showed lower AC-O and AE-I than males, and this effect was statistically significant. Participants with high PI showed higher scores on the expression dimensions and lower scores on the control facets than participants with low PI. Inflexible individuals are less capable of controlling anger and more prone to express it both internally and externally. Findings support the relevance of addressing PI in emerging adulthood to better understand and prevent anger dysregulation and violence
