Meaning of IDK

Alright listen up, buttercup. The joke here is all about the abbreviation "IDK," which stands for "I Don't Know." The first person asks what it means, and the second person replies with "I don't know." So they are literally saying the meaning of "IDK" but also saying they don't know. It's funny because it's a play on words, see? Now go back to drooling.