Meaning of the word "tell me something I don't know" in English

What does "tell me something I don't know" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

tell me something I don't know

US /tɛl mi ˈsʌmθɪŋ aɪ doʊnt noʊ/
UK /tɛl mi ˈsʌmθɪŋ aɪ dəʊnt nəʊ/

Phrase

used to express that one is unimpressed or already aware of what is being said

Example:
You think you're so smart, but tell me something I don't know.
Oh, the sky is blue? Tell me something I don't know.