The Chinese idiom "大言不惭" is formed by directly combining four characters: "大" meaning big or grandiose, "言" meaning speech or words, "不" meaning not, and "惭" meaning ashamed. These characters are arranged in a sequential structure where "大言" (grandiose speech) serves as the subject, and "不惭" (not ashamed) acts as the predicate, creating a literal meaning of "grandiose speech is not ashamed", which functions as a fixed expression to describe someone who boasts without embarrassment.