The word "蹭吃蹭喝" is formed by repeating the verb "蹭" (meaning to freeload) in conjunction with the verbs "吃" (to eat) and "喝" (to drink), creating a compound where "蹭吃" denotes freeloading meals and "蹭喝" denotes freeloading drinks, together representing the act of sponging off others for both food and beverages.