The idiom "出言不逊" is formed by sequentially combining the characters 出 (to utter), 言 (words), 不 (not), and 逊 (humble), where the verb phrase "出言" (to speak out) is directly modified by the adjective phrase "不逊" (not humble), resulting in a literal meaning of "to speak out words that are not humble", thus expressing the act of making insolent remarks.