Slang usage in modern age Iran is a popular phenomenon among most male and female teenagers. How pervasive this variation of language use is among various age and sex groups in Iran has been a question of debate given the significance of religion in a theological system of social structure. The work presented in this study aims to investigate the effect of age and sex on variability of slang usage. Sixty Iranian participants were selected, and then were divided into three age groups (i.e. primary school, high school, and senior university students) each group consisting of ten males and ten females. A self-made questionnaire in the form of Discourse Completion Test (DCT) describing nine situations of friendly conversations was given to the participants. They were asked to make their choice on the responses, which ranged from formal to very informal style (common teenage slang expressions), or to write down what they wish to say under each circumstance. The results of the chi–square tests indicated that slang usage among high school students is more frequent as compared with other age groups. Unlike the popular belief suggesting that slang is used by boys rather than girls, the findings suggested that young Iranians both male and female use slang as a badge of identity showing their attachment to the social group they wish to be identified with.