This study explores whether aggressive text-based interactions in social media are contagious. In particular, we examine swearing behaviour of YouTube commentators in response to videos and comments posted on the official Donald Trump's campaign channel. Our analysis reveals the presence of mimicry of verbal aggression. Specifically, swearing in a parent comment is significantly and positively associated with the likelihood and intensity of swearing in subsequent 'children' comments. The study also confirms that swearing is not solely a product of an individual speech habit but also a spreadable social practice. Based on the findings, we conclude that aggressive emotional state can be contagious through textual mimicry.