Swearing uses language forms that are taboo and potentially offensive. These are often used for emotional expression. Multilingual research shows that because the first language retains most emotional force (Dewaele [2004]. "The Emotional Force of Swearwords and Taboo Words in the Speech of Multilinguals." "Journal of Multilingual and Multicultural Development" 25 (2/3): 204-219; Pavlenko [2012]. "Affective Processing in Bilingual Speakers: Disembodied Cognition?" International Journal of Psychology 47 (6): 405-428), it is often the language of choice for swearing. Furthermore, swearing frequency and language preference are associated with different personality traits (Dewaele [2017a]. "Self-Reported Frequency of Swearing in English: Do Situational, Psychological and Socio-Biographical Variables Have Similar Effects on First and Foreign Language Users?" "Journal of Multilingual and Multicultural Development" 38 (4): 330-345). This study draws together these multilingualism research areas to investigate Persian immigrants' language choice for swearing, with reference to personality traits and socio-biographical factors, and in light of the Iranian cultural context. A mixed methods approach was adopted combining questionnaire and interview data. 204 Persian-English multilinguals residing outside Iran participated. Key findings revealed nuanced gender and personality dimensions. Specifically, women with higher Social Initiative (Extraversion) used English swearwords more frequently than Persian swearwords. Men who showed lower Emotional Stability (high Neuroticism) used Persian swearwords more frequently than English swearwords. There was also a positive relation between frequency of the use of Persian/English, self-rated knowledge in Persian/English, and Cultural Empathy and Open-mindedness. Semi-structured interviews provided deeper insight into these language choices. The study highlights how language preferences for swearing are shaped by both personality and socio-biographical factors in complex and nuanced ways.