Internet trolling is a provocative or offensive online behavior linked to engaging in anonymous activities that evoke negative feelings in other people. We analyzed the relationships between Internet trolling, Dark Triad traits (i.e., psychopathy, narcissism, and Machiavellianism), and the Behavioral Inhibition System (BIS)/Behavioral Approach System (BAS) in two studies. Study 1 involved a national quota sample representative of Polish young adults (N = 1,048, aged 18–25), and Study 2 involved a national quota sample of adult Poles (N = 432, aged 18–84). In both studies, we hypothesized and found that Internet trolling is predicted by low BIS and high BAS and that these relationships are mediated by high levels of psychopathy. These findings suggest that the basic temperamental dispositions may predispose individuals to irritate others on the Internet for one’s own enjoyment due to high (vs. low) levels of psychopathy. We discuss the role of temperamental and personality traits in shaping offensive online behavior.