On the Internet, many commentary styles take place on various forums, and abuse is not uncommon. We investigated the personality traits related to individuals’ behaviors on Internet forum posting. The Dark Short Tetrad (SD4) were used to predict (N = 212) three types of commentary styles: Trolling (malicious posting), Lurking (reading/not posting) and Posting (reading/posting). The results showed that Trolling co-varied with Sadism (r = .38) and Machiavellianism (r = .28). The results also showed that people high on dark traits are Trolling the Internet. Exploratory mediator analyses further revealed that various aspects of anonymity trivially moderate personality traits and behavior (indirect effects β ≈ .10). The overall take-home message is that personality traits, especially dark traits, play a role in how individuals express themselves online. This provides well-needed insight in abusive behaviors in forums on the internet.