An analysis of data collected from 2347 users of English on their self-reported swearing behaviour in English revealed significant higher values for the 1159 native English (L1) users than for the 1165 English foreign language (LX) users. Parallel analyses on the data of the L1 and LX users revealed that the interlocutor effect was slightly stronger among L1 users. Swearing was reported to be most frequent in interactions with friends, when alone, followed by interactions with family members, colleagues and strangers. Participants scoring high on Psychoticism, Extraversion and Neuroticism reported significantly more swearing in English. Extraversion and Neuroticism had the strongest effects on LX users' self-reported swearing with friends and alone while Psychoticism and Neuroticism had the strongest effects on L1 users' self-reported swearing with strangers and with friends. The effects of sociobiographical variables (education level, age group, gender) were broadly similar among L1 and LX users but were significant in more categories of interlocutors for the L1 users. It is argued that the weaker effect of situational, psychological and sociobiographical variables on self-reported frequency of swearing among LX users of English could be linked to larger heterogeneity in their history of learning, socialisation, proficiency and use of English.