얼굴에 철판 깔다.

The idiom '얼굴에 철판 깔다' (eolgure cheolpan kkalda) literally translates to 'to lay a steel plate on one's face.' This vivid imagery directly conveys the meaning of acting boldly or shamelessly without feeling embarrassed or guilty. The 'face' (얼굴, eolgul) in Korean culture is strongly associated with honor, dignity, and a sense of shame or propriety. To 'lay a steel plate' (철판 깔다, cheolpan kkalda) on it suggests making one's face impervious to such feelings, effectively creating a barrier against shame or embarrassment. The origin of this idiom isn't tied to a specific historical event or a single author, but rather evolved organically within the Korean language to express a commonly observed human behavior. It likely emerged from a time when the concept of 'saving face' and maintaining social decorum was highly emphasized. Someone who 'lays a steel plate on their face' is seen as defying these social expectations, behaving in a way that would normally cause embarrassment, but doing so without any apparent compunction. The idiom effectively captures the essence of a person who is brazen, impudent, or thick-skinned. It's often used with a negative connotation, describing someone who acts selfishly, manipulatively, or in a way that disregards the feelings of others. The strength and impermeability of 'steel plate' metaphorically amplify the degree of their shamelessness. Similar expressions exist in other languages, such as 'to have a thick skin' in English, but '얼굴에 철판 깔다' offers a more visually striking and culturally specific depiction of the phenomenon. The phrase highlights the contrast between expected social behavior and the individual's unashamed actions, making it a powerful and commonly understood idiom in contemporary Korean.