Despite the rise in the number of researches regarding cyberbullying among children and youth, as well as the relationship of bullying with moral and personality, little is known about the same constructs among adults. The aim of this research was to investigate the frequency of committing certain negative behavior on social networks (NPDM) and the relationship of stated with moral reasoning, moral disengagement and personality traits. The data was collected through an online Google Docs survey on a suitable sample of adults between the ages of 18 and 62 (N = 391). The participants completed the Cyberbullying Scale, IPIP 50S, Short Dark Triad scale, Moral Reasoning Test and Propensity to Morally Disengage Scale. The results showed that adults, just like young people, participate in various ways in NPDM and that the involvement in these behaviors decreases with age. As with young people, the most common behaviors include gossiping and ridiculing others, and the least common include sharing pictures of sexual content, forcing others to talk about sex and breaking into someone else's profile. Those individuals who achieve higher scores on the Dark Triad scale, lower scores on the Conscientiousness, Agreeableness and Emotional Stability scales and are more prone to moral disengagement are more likely to engage in various NPDM’s. Furthermore, a moderating role of moral reasoning was not found in explaining NPDM's relationship with personality. On the other hand, the propensity to moral disengagement was found to play a moderating role in explaining the relationship between Agreeableness and Emotional Stability with NPDM. The relationship of the mentioned variables was significant in the group of individuals with a lower propensity for moral disengagement (negative correlation), but not in the group of individuals with greater preference towards moral disengagement.