On 24th July 2013, feminist campaigner Caroline Criado-Perez's petition to the Bank of England to have Elizabeth Fry's image on the UK's £5 note replaced with the image of another woman was successful. The petition challenged the Bank of England's original plan to replace Fry with Winston Churchill, which would have meant that no woman aside from the Queen would be represented on any UK banknote. Following this, Criado-Perez was subjected to ongoing misogynistic abuse on Twitter, a microblogging social network, including threats of rape and death. This paper investigates this increasingly prominent phenomenon of rape threats made via social networks. Specifically, we investigate the sustained period of abuse directed towards the Twitter account of feminist campaigner and journalist, Caroline Criado-Perez. We then turn our attention to the formation of online discourse communities as they respond to and participate in forms of extreme online misogyny on Twitter. We take a corpus of 76,275 tweets collected during a three month period in which the events occurred (July to September 2013), which comprises 912,901 words. We then employ an interdisciplinary approach to the analysis of language in the context of this social network. Our approach combines quantitative approaches from the fields of corpus linguistics to detect emerging discourse communities, and then qualitative approaches from discourse analysis to analyse how these communities construct their identities.