Based on the social-cognitive information processing model and the theory of normative beliefs, this study tests if gamers normalise aggression in games, and whether these normative beliefs explain their aggressive behaviour in games. Experimental cross sectional, worldwide data was collected through an online survey of gamers (N = 1646). Participants were randomly assigned to read a vignette describing an instance of verbal harassment occurring either online (within a multiplayer game) or offline (within a board game café) and were asked how acceptable and tolerable they found the harassment. There was a significant moderate main effect of context which indicated that harassment was perceived as more normal in the online gaming scenario. Normative beliefs about cyberaggression significantly predicted both general and prejudiced cyberaggression. Additionally, normative beliefs partially mediated the relationship between age and general cyberaggression (small effect) and gender and general cyberaggression (large effect). As normative beliefs are dynamic and modifiable, cyberaggression prevention and intervention efforts should include modification of beliefs which support the legitimacy and acceptability of cyberaggression in games. These findings provide insight into how gamer culture around acceptability of trash talk relates to toxicity in games and suggest directions for further research.