I can't remember where I got this from, but it feels deeply correct to me. However it caused a misunderstanding in a chat, and after googling the usage and not finding anything I'm suspecting I might be using it wrong.
So in my mind, given the right context "guess what" can be equivalent to "Oh, interesting, who'd have thought that". Like in
Them: Did you hear about it, Adam and Eve got married today.
Me: Guess what!
So I'm saying "guess what" to express my feeling of surprise, not because I actually want them to guess something. Is this usage valid?
Best Answer
It is the other way around. "Guess what! Adam and Eve got married today."
To show your surprise, you can use "No kidding!"
See Merriam Webster:
Edit: Lambie raises an interesting point about punctuation marks. In writing a question mark following "guess what" is indeed common, but I wouldn't call the exclamation mark a mistake. In speech it is rarely if ever uttered in a rising tone. The fact that the exclamation mark is also not uncommon in writing reflects this.