This study aimed to develop the Global Assessment of Active Trolling and Passive Bystanderism (GAATPB) scale and investigate the influence of personality traits on trolling behaviors. Focusing on the Dark Tetrad (DT) traits and agreeableness, the present study examined their associations and predictive utility on active trolling and passive bystanderism. Participants were recruited from social networking sites (SNSs), and eligibility criteria included active SNS usage and engagement in online interactions. A total of 797 healthy adult students participated in the study, with data from 300 used for the initial exploratory factor analysis (EFA) and the remaining 497 (Mage = 22.25 years, SD = 3.37) for the subsequent analyses. Results indicated a significant correlation between DT traits and agreeableness across both active trolling and passive bystanderism, revealing a shared personality profile. Hierarchical multiple regression analyses showed that narcissism, Machiavellianism, and trait sadism were predictors of active trolling, with psychopathy being the strongest predictor. However, psychopathy did not emerge as a predictor for passive bystanderism. The study also highlighted that DT traits mediated the relationship between lower agreeableness and overall trolling behavior, suggesting that trolling manifests from lower agreeableness through the instigation of callous-unemotional, manipulative, and self-centered traits inherent in DT.