When someone writes af (either capitalized or in lowercase letters) on social media or in a text message, it simply translates to as f***.
Mgbe mmadụ na-ede af (ma ọ bụ n'isi ma ọ bụ na obere mkpụrụedemede) na mgbasa ozi mmadụ ma ọ bụ na ozi ederede , ọ na-sụgharịa dịka F *** .