This paper examines the use of slang as a means of excluding those outside the social circle(s) of selected undergraduates of the Ahmadu Bello University, Zaria from their in-group communication. The paper begins by looking at how users of language manipulate it to meet their communication needs leading to the evolution of several varieties which apart from meeting these needs, also become a form of identity for such users. Thereafter, the paper examines English slang as one of such varieties from its initially restricted use to its prevalence among Nigerian undergraduates in general and those of the Ahmadu Bello University, Zaria in particular while also appraising its various definitions put forward by some linguists. In addition, the paper discusses its methodology especially the three research instruments (involving questionnaires, spontaneous interviews and non-participatory observation) used for data collection from randomly selected undergraduates of the institution across four faculties namely: Faculty of Arts, Education, Engineering and Social Sciences. Drawing from the data obtained through the aforementioned instruments and its subsequent analysis, the paper discusses the findings which proved that slang is a veritable tool among the target population who do not only use it as a powerful means of communication and identity enhancement but also, as a way of shutting out those whom they do not want to be part of their in-group communication. The findings also showed that, those who were mostly excluded from the in-group communication of the subjects of this study through the use of coded slang words were lecturers, invigilators and female students. The paper concludes that, slang as used by the subjects of the study is not just a symbol of identity, but a potent tool that empowers them to either open the door to ‘outsiders’ to partake of their communication or shut it against them through the use of special slang words.